Faculty Profiles - SHIOKAWA, Kazuo

Study of the Mid-Latitude Airglow Responses to Geomagnetic Storms Based on Long-Term Observations in Japan With the TIMED Satellite and Ionosondes Reviewed Open Access

Hotta Y., Shiokawa K., Otsuka Y., Nishioka M., Yue J.

Journal of Geophysical Research Space Physics Vol. 131 ( 3 ) 2026.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

Variations in nighttime airglow at mid-latitudes during geomagnetic disturbances reflect the propagation of atmospheric and plasma disturbances from polar heating as well as local chemical processes. However, their detailed mechanisms remain unclear. In this study, we analyzed the responses of six nighttime airglow emissions to geomagnetic storms using data from airglow temperature photometers at three locations in Japan (Rikubetsu (43.5°N, 143.8°E), Shigaraki (34.8°N, 136.1°E), and Sata (31.0°N, 130.7°E)) over a long-term period from January 2004 to October 2023. The emissions include the OH Meinel band, O<inf>2</inf> atmospheric band, O (557.7 nm), Na (589.3 nm) from the mesopause region, and O (630.0 and 777.4 nm) from the thermosphere. The main results show an increase in the intensity of the 557.7-nm emission 2 days after geomagnetic storms in the mesopause region and an increase in the 630.0-nm emission 1 day after storms in the thermosphere. Similar responses were observed in the O<inf>2</inf> atmospheric band (mesopause region) and the 777.4-nm emission (thermosphere) to those of 557.7-nm and 630.0-nm emissions, respectively. No significant changes were found in the rotational temperatures of OH and O<inf>2</inf>. The SABER instrument onboard the TIMED satellite observed a post-storm increase in the atomic oxygen mixing ratio at altitudes of 90–100 km. We suggest that this atomic oxygen increase contributed to the enhanced 557.7-nm emission in the mesopause region. Ionosondes over Japan observed rise of ionospheric altitudes and enhancements of foF2 1 day after storms. We discuss their possible relation to the observed thermospheric 630.0-nm emission enhancements.

DOI： 10.1029/2025JA034616

Wind Induced F3 Layer in the Middle Latitude During the Mother's Day Geomagnetic Disturbances of 10–11 May 2024 Reviewed Open Access

Rai B., Kalita B.R., Bhuyan P.K., Otsuka Y., Shiokawa K., Pallamraju D.

Journal of Geophysical Research Space Physics Vol. 131 ( 2 ) 2026.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

The formation process of the F3 layer at sunrise in the middle latitudes is newly investigated using data from the Mother's Day geomagnetic storm of 10–11 May 2024. Ionosonde, Fabry-Perot Interferometer (FPI), satellite data, and model simulations of Equatorial Electric Field for India, South-East Asia-Australia, and Japanese sectors are utilized. The F3 layer was recorded by Ionosondes at Japanese mid-latitude stations during 19 UT–21 UT, which coincided with the local Sunrise time. Over Perth (Australia), Wuhan (China), and Ahmedabad (India), formations were delayed at 22 UT–23 UT. The COSMIC vertical profiles showed enhanced F2 layer altitude after 19 UT, and confirmed the formation of additional ionospheric stratifications above the F2 layer. The thermospheric winds measured by FPI at northern mid-latitude and southern low-latitudes indicated strong equatorward winds in both hemispheres starting around 18:30 UT. The analysis revealed that dawn-time F3 layer stratifications in middle latitude were manifestations of residual nighttime F layer, which was raised to higher altitude by the equatorward winds, even as a new weak F2 layer was formed below by photo-ionization. The reduction in thermospheric O/N<inf>2</inf> caused the F3 layer at higher altitudes to survive and remain stronger than the F2 layer for a considerable time after sunrise. In contrast, the low-latitude F3 layer was formed by vertical drift induced by the electric field, when an IMF-Bz transition resulted in an eastward penetration electric field pulse in the dawn sector. At Perth in the southern hemisphere, both mechanisms were effective in the formation (wind) and sustenance (electric field) of the F3 layer.

DOI： 10.1029/2025JA034833

Power attenuation of Pc1 waves during propagation from the magnetosphere to the ionosphere observed by the Arase satellite and PWING ground stations Reviewed Open Access

Jaeyoung Kwak, Chae-Woo Jun, Yukinaga Miyashita, Jaeheung Park, Yoshizumi Miyoshi, Kazuo Shiokawa, Ayako Matsuoka, Mariko Teramoto, Kazuhiro Yamamoto, Iku Shinohara, Yoshiya Kasahara, Fuminori Tsuchiya, Atsushi Kumamoto, Atsuki Shinbori, Dmitry Baishev, Igor Poddelsky

Earth, Planets and Space 2026.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

Understanding how the properties of Pc1 waves change during their propagation from the magnetospheric source regions to the middle or low-latitude ionosphere have not yet been clearly revealed by observations. In this study, we present the first quantitative comparison of Pc1 wave power attenuation both along the geomagnetic field lines and in the ionospheric wave ducts, using simultaneous observations from the Arase satellite and dynamical variation of Particles and Waves in the INner magnetosphere using Ground-based network observations (PWING) ground magnetometers. One of our key findings is that the polarization sense of the waves changed from left-handed polarization (LHP) at the satellite to right-handed polarization (RHP) on the ground, providing observational evidence of polarization transformation from space to the ionosphere. By examining polarization angles, we confirm that the Pc1 waves observed at multiple ground stations originated from the same magnetospheric source as the EMIC waves detected by the Arase. Importantly, we quantify the wave power attenuation factor along the magnetic field line to be only 0.37 dB/1000 km, which is nearly an order of magnitude smaller than that in the ionospheric wave duct (4.7–8.2 dB/1000 km). This result establishes a previously unreported minimum Pc1 wave attenuation rate in the magnetosphere, highlighting that the wave energy loss occurs more rapidly in the ionospheric duct than in space. These findings provide new insights into Pc1 wave transmission mechanisms and emphasize the importance of combined space- and ground-based observations for characterizing wave propagation processes across geospace.

Graphical Abstract

DOI： 10.1186/s40623-026-02372-4

Characteristic behavior of SAR arc, STEVE and Red-Green arc during HILDCAA events Reviewed

Nema A., Shiokawa K., Connors M., Pathak K.N., Datta A.

Advances in Space Research 2026

Language：English Publishing type：Research paper (scientific journal) Publisher：Advances in Space Research

Using 630.0 nm all-sky airglow imagers at Athabasca (Canada), Kapuskasing (Canada) and Nyr(Formula presented) l(Formula presented) (Finland), we present the first statistical analysis of the Stable Auroral Red (SAR) arcs, STEVE, and Red-Green (RG) arcs during High-Intensity Long-Duration Continuous AE Activity (HILDCAA) events from 2011 to 2019. These optical phenomena are unique and relatively faint subauroral optical phenomena observed in the Earth’s upper atmosphere at subauroral latitudes. We discovered 25 subauroral optical phenomena (SAR arc, STEVE, and Red-Green arc) after analyzing all-sky images taken over the 9-years period. The arc detachments from the auroral oval typically occur in the premidnight sector, indicating ring current ion drift to the dusk sector. Out of total 12 HILDCAA events, from 2011 to 2019, more than 90 % were accompanied by at least one of these auroras. We also found that the auroras occurring during these HILDCAA events tends to happen predominantly during midnight hours. The occurrence rate of these auroras found to be much higher during HILDCAA events reaching to approximately 45 %, compared to previous statistical studies, including non–HILDCAA times.

DOI： 10.1016/j.asr.2026.01.076

COURSE: Cross-scale cOUpling pRocesses in the Solar–tErrestrial system—SCOSTEP’s new program for 2026–2030 Reviewed Open Access

Laurenza M., Shiokawa K., Molina M.G., Liu H.L., Krivova N.A., Funke B., Kusano K., Habarulema J.B., Buresova D., West M.J., Chau J., Zhang J., Nesse H., Usoskin I., Alberti T., Alfonsi L., Coddington O., Dasso S., Fung S.F., Hayakawa H., Miyoshi Y., Nakamura R., Temmer M., Stolle C., Zong Q.G., Briand C., Goplaswamy N., Safranova J.

Earth Planets and Space Vol. 77 ( 1 ) 2025.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Earth Planets and Space

The committee nominated to define the Scientific Committee on Solar–Terrestrial Physics (SCOSTEP) Next Scientific Program (NSP) has identified cross-scale coupling as the overarching theme for conducting and promoting coordinated research and outreach activities in the upcoming period 2026–2030. The program is called COURSE (Cross-scale cOUpling pRocesses in the Solar–tErrestrial system) and is organized in three main scientific focus areas: 1) sources of space weather and space climate; 2) solar wind, magnetosphere, and ionosphere coupling; and 3) external impacts and internal dynamics of the Earth atmosphere. For each Focus Area the NSP committee has identified: 1) long-standing goals, i.e., key questions persistent through SCOSTEP scientific programs and 2) objectives, i.e., precise outcomes that can be addressed over the 5-year program duration, which contribute to achieving the goals over the long term. Moreover, the committee envisions the implementation of the program through identified novel methods, including machine learning and Artificial Intelligence techniques; integrated models; new missions; the combination of multipoint in-situ data with ground observations; improved metadata; and adoption of Findable, Accessible, Interoperable, and Reusable (FAIR) principles.

DOI： 10.1186/s40623-025-02283-w

Effects of Field Line Curvature Scattering on Energetic Proton Precipitation and Isotropy in the Magnetosphere Reviewed Open Access

S. Imajo, Y. Miyoshi, S. Kasahara, S. Yokota, A. Matsuoka, K. Keika, T. Hori, I. Shinohara, K. Shiokawa, K. Yamamoto, M. Teramoto

Journal of Geophysical Research: Space Physics Vol. 130 ( 11 ) 2025.11

Language：English Publishing type：Research paper (scientific journal) Publisher：American Geophysical Union (AGU)

Abstract

While low‐altitude observations indicate that field line curvature (FLC) scattering produces isotropic precipitation of energetic protons, it remains unclear whether this mechanism also leads to a fully isotropic pitch angle distribution in the magnetosphere. In this study, we distinguished the low‐latitude boundaries of the loss cone filling and the isotropic distribution of energetic protons in an energy range of 10–180 keV using middle‐altitude (3–5 ) off‐equatorial observations made by the Arase satellite. The isotropic distribution boundary (IDB) is defined by the ratio of proton fluxes at pitch angles of 0°–45° to 45°–90° for the northern hemisphere. The latitude of the IDB exhibits energy dependence, such that higher energy protons become isotropic at lower latitudes, implying isotropization of protons by FLC. Around the IDB, the downward loss cone was filled, while the corresponding upward loss cone was empty due to atmospheric loss. The low‐latitude boundary of the loss cone filling tended to be located at 0.1°–0.4° lower latitude than the IDB. Numerical simulations using the centrifugal impulse model for FLC scattering reproduced this latitude difference in the low‐latitude boundaries of the loss cone filling and the isotropic distribution. These results suggest that effective pitch angle scattering occurs only near the loss cone on the field line with a larger equatorial curvature radius, resulting in loss cone filling, whereas it occurs more broadly across the pitch angles on the field line with a smaller equatorial curvature radius, leading to the isotropic distribution.

DOI： 10.1029/2025ja034307

Estimate of (Formula Presented) Altitude Profile Using Blue Auroral Resonant-Scattering 427.8 nm Emission Observed With HySCAI During Astronomical Twilight Reviewed

Ida K., Yoshinuma M., Ebihara Y., Shiokawa K.

Geophysical Research Letters Vol. 52 ( 21 ) 2025.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Geophysical Research Letters

The spectrum of high-altitude blue auroral emissions was observed with HyperSpectral camera for auroral imaging (HySCAI) during morning astronomical twilight in Kiruna. Auroral resonance scattering of an (Formula presented.) 1NG (0, 1) (427.8 nm) emission starts to increase from the east, and then the increase of this resonance scattering emission extends to the magnetic zenith. The volume emission rate is evaluated from the rise in resonance scattering emission (time derivative of emission intensity). The volume emission rate of (Formula presented.) (427.8 nm) reaches its maximum when the sunlight shadow height reaches 200 km, although the GLOW model predicted a peak altitude of (Formula presented.) (427.8 nm) of 120 km. The higher altitude of the resonance scattering emission peak observed with HySCAI supports the idea that (Formula presented.) is produced by the charge exchange between (Formula presented.) and (Formula presented.) existing at high altitudes. However, we cannot rule out another possible mechanism of upflowing (Formula presented.) ions.

DOI： 10.1029/2025GL118375

Multiple-Event Study of Substorm Electric Field Penetration Into Middle Latitudes Based on Simultaneous Observation of 630-nm Airglow Enhancements at Three Stations Reviewed

Medium-Scale Traveling Ionospheric Disturbances Observed by Nadir-Viewing 630 nm Airglow Imaging From the International Space Station Reviewed Open Access

Yuta Hozumi, Akinori Saito, Michi Nishioka, Takeshi Sakanoi, Jia Yue, Min-Yang Chou, Satoshi Andoh, Atsushi Yamazaki, Yuichi Otsuka, Kazuo Shiokawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 130 ( 10 ) 2025.10

Morita S., Shiokawa K., Otsuka Y., Nshitani N., Shinbori A., Fujimoto A., Yoshikawa A., Nishioka M., Perwitasari S., Yamamoto M., Sori T.

Journal of Geophysical Research Space Physics Vol. 130 ( 10 ) 2025.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

It is known that convection electric fields develop in the polar region associated with substorm onset, and a westward electric field penetrates to lower latitudes on the night side. Two-dimensional observations of 630-nm airglow enhancements associated with the westward electric field can be conducted using all-sky cameras at middle latitudes. We investigated seven simultaneous 630-nm airglow enhancement events using all-sky cameras at Rikubetsu (43.5°N, 143.8°E), Shigaraki (34.9°N, 136.1°E), and Sata (31.0°N, 130.7°E) in Japan. A multi-event multi-point study of 630-nm airglow enhancement has been conducted for the first time. These seven events were found from 1,800 nights in 11 years, from 2002 to 2012, indicating that simultaneous 630-nm airglow enhancements over Japan were very rare. Five of these events occurred during storms, suggesting that simultaneous enhancement requires a large penetrating electric field associated with storm-time substorms. In three events, the enhancement was identified as occurring simultaneously with clear substorm onsets, while the other four events were also associated with high-latitude magnetic disturbances. In all seven events, we observed downward motion of the ionosphere associated with the airglow enhancement. These results indicate that they are due to the westward electric field in the substorm undershielding state. In two events, the time at the end of the 630-nm airglow enhancement correlated well with the increase in ionospheric altitude observed by ionosondes and an FM-CW radar. This increase in ionospheric altitude and termination of the airglow enhancement could be caused by eastward electric field penetration associated with overshielding in the magnetosphere.

DOI： 10.1029/2025JA033721

Evolution and decay of a stable and a dynamic airglow patch Reviewed

Eriksen N.K., Nishimura Y., Zettergren M., Lorentzen D.A., Oksavik K., Baddeley L.J., Hosokawa K., Shiokawa K., Lamarche L., Redden M.E., Bhatt A.

Journal of Atmospheric and Solar Terrestrial Physics Vol. 275 2025.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Atmospheric and Solar Terrestrial Physics

This study investigates the evolution of two polar cap airglow patches, AGP1 and AGP2, observed over Resolute Bay in northern Canada. AGP1 exhibited stable shape, followed the ExB drift patterns and maintained high electron density as it transited toward the auroral oval, sustaining the maximum F-region density and redline emissions by a downward vertical drift. An initial non-uniform density decay was observed in AGP1’s density profile; the topside shifted downwards, resulting in increased bottomside density. Later, the maximum and bottomside density started to decay. Overall, the downflow contributed to a faster density decay. In contrast, AGP2 displayed dynamic characteristics, halting its motion mid-polar cap, followed by a prolonged decay in both electron density and redline emission. Observations and GEMINI simulations revealed that recombination between atomic ions and neutral molecules was the dominant mechanism for density decay in the optical layer. The decay rate was affected by vertical drift, magnetic field line orientation, and local neutral atmosphere conditions, which may be influenced by prior patch activity. Simulations of AGP1 using GEMINI and GLOW highlight the importance of vertical ExB drift in sustaining electron density maximum and redline emission intensity. By using various free parameters in the model to tune our simulations (e.g. background precipitation) we are able to achieve reasonable agreement with observed patch behavior. Our findings emphasize the interplay between vertical drift, recombination rates, and neutral wind in determining polar cap patch evolution, as well as the complexity of patch dynamics and their dependence on local ionospheric and atmospheric conditions.

DOI： 10.1016/j.jastp.2025.106593

Machine Learning Recognition and Phase Velocity Estimation of Atmospheric Gravity Waves from OI 557.7 nm All-Sky Airglow Images Reviewed Open Access

Mahmoud R., Abdelwahab M., Shiokawa K., Mahrous A.

AI Switzerland Vol. 6 ( 10 ) 2025.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AI Switzerland

Atmospheric gravity waves (AGWs) are treated as density structure perturbations of the atmosphere and play an important role in atmospheric dynamics. Utilizing All-Sky Airglow Imagers (ASAIs) with OI-Filter 557.7 nm, AGW phase velocity and propagation direction were extracted using classified images by visual inspection, where airglow images were collected from the OMTI network at Shigaraki (34.85 E, 134.11 N) from October 1998 to October 2002. Nonetheless, a large dataset of airglow images are processed and classified for studying AGW seasonal variation in the middle atmosphere. In this article, a machine learning-based approach for image recognition of AGWs from ASAIs is suggested. Consequently, three convolutional neural networks (CNNs), namely AlexNet, GoogLeNet, and ResNet-50, are considered. Out of 13,201 deviated images, 1192 very weak/unclear AGW signatures were eliminated during the quality control process. All networks were trained and tested by 12,007 classified images which approximately cover the maximum solar cycle during the time-period mentioned above. In the testing phase, AlexNet achieved the highest accuracy of 98.41%. Consequently, estimation of AGW zonal and meridional phase velocities in the mesosphere region by a cascade forward neural network (CFNN) is presented. The CFNN was trained and tested based on AGW and neutral wind data. AGW data were extracted from the classified AGW images by event and spectral methods, where wind data were extracted from the Horizontal Wind Model (HWM) as well as the middle and upper atmosphere radar in Shigaraki. As a result, the estimated phase velocities were determined with correlation coefficient (R) above 0.89 in all training and testing phases. Finally, a comparison with the existing studies confirms the accuracy of our proposed approaches in addition to AGW velocity forecasting.

DOI： 10.3390/ai6100262

Strong Substorm Development From Polar-Cap Arc Laydown Along the Auroral Poleward Boundary Reviewed

Lyons L.R., Nishimura Y., Liu J., Yadav S., Zou Y., Bristow W.A., Donovan E., Nishitani N., Shiokawa K., Hosokawa K.

Journal of Geophysical Research Space Physics Vol. 130 ( 10 ) 2025.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

Meso-scale enhanced flow channels often extend across the polar cap from the dayside to the nightside auroral oval, where they enter the oval via localized reconnection and cause auroral oval disturbances. Examples here show such flows associated with azimuthally moving polar cap arcs that develop an equatorward portion that bends in the direction opposite to the arc's motion, becoming nearly parallel to the nightside auroral oval and possibly becoming an oval poleward boundary arc. The arcs then continue to move equatorward, and “lay down” along the auroral oval, leading to an explosive substorm onset (or expansion enhancement) that rapidly expands azimuthally with laying down of the arc, and later expands further with westward traveling surge sliding along the arc. This gives a longitudinally broad region of expansion-phase aurora, and a similarly broad magnetic depression, indicating large and broad substorm energy release. The surge sliding along the poleward boundary arc occurs at a higher latitude than the laydown portion of onset, so that sliding leads to later magnetic depressions at locations west of the initial onset and at higher latitudes. The polar cap arc appears to be pushed equatorward and westward (for By >0) by the flow of new plasma moving across the polar cap, the arc being like a weather front that demarcates an advancing boundary between plasma regimes along polar cap field lines. The onset and expansion of the activity appear to be driven by the flow of this new plasma from the polar cap to the region of expansion phase activity.

DOI： 10.1029/2025JA034161

Reduction of High Latitude Ionospheric Electron Density by the Impact of Negative Solar Wind Pressure Pulse During the Geomagnetic Storm of 23 March 2023 Reviewed Open Access

Geetashree Kakoti, Mala S. Bagiya, Geeta Vichare, Kazuo Shiokawa, P. R. Shreedevi, Nozomu Nishitani, Yuichi Otsuka, Atsuki Shinbori, Michi Nishioka, Septi Perwitasari

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 130 ( 8 ) 2025.8

Strong Westward Current Pulse at Auroral Latitudes Extending to Dawn-Side Low-Latitudes Due To Enhanced Density Within Kelvin-Helmholtz Wave Vortex in Solar Wind Reviewed Open Access

Nilam B., Tulasi Ram S., Oliveira D.M., Remya B., Shiokawa K., Rai D., Sibeck D., Dimri A.P.

Geophysical Research Letters Vol. 52 ( 15 ) 2025.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Geophysical Research Letters

A series of coronal mass ejections (CMEs) from the Sun, interacted with one another and formed a complex interplanetary-CME (ICME) that impinged Earth's magnetosphere on 10 May 2024 and caused the strongest geomagnetic storm of the past two decades. We present a unique pulse-like enhanced solar wind density structure associated with a giant Kelvin-Helmholtz (KH) wave vortex formed within the ICME due to compression of sheath region by the surrounding ejecta. When impinged on the magnetosphere, it caused enhanced eastward and westward currents, leading to strong positive and negative geomagnetic field impulses at low and auroral latitudes, respectively. The negative disturbances extended to mid-latitudes around the midnight sector. Interestingly, the westward current pulse (negative disturbance) penetrated deep into low-latitudes (up to 24.49°N and 28.92°S) in both hemispheres, but exclusively on the dawn side. The mechanisms responsible for such an intensification and low-latitude penetration of westward current pulse are discussed.

DOI： 10.1029/2025GL117032

Ionospheric Scintillation and Geomagnetic Disturbance Caused by Space Hurricanes Reviewed Open Access

Lu S., Xing Z.Y., Zhang Q.H., Zhang Y.L., Yang H.G., Oksavik K., Lyons L.R., Shiokawa K., Wang Y., Ma Y.Z., Wang X.Y., Xu T., Sun S.J., Zhang D.

Space Weather Vol. 23 ( 7 ) 2025.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Space Weather

A space hurricane is a large-scale, cyclone-shaped aurora characterized by a rotating magnetic structure and shears in plasma convection, driven by high-latitude magnetic reconnection. It typically forms near the magnetic poles in summertime, providing an efficient energy transport channel from the solar wind to the Earth's magnetosphere under northward interplanetary magnetic field conditions. Here, we present a detailed case study of a typical space hurricane that occurred on 20 August 2014 and its impact on the polar ionosphere in the Northern Hemisphere. Multi-instrument observations from the Eureka GNSS receiver, SWARM and Defense Meteorological Satellite Program (DMSP) satellites indicate that GPS signals experienced enhanced phase scintillation near a space hurricane, coinciding with regions of large plasma density gradients and flow shears. Based on these in situ measurements, we estimated growth timescales of ∼94 s for gradient-drift instability and ∼352 s for KHI, supporting the plausibility of both instabilities. These plasma instabilities likely generated small-scale irregularities responsible for the observed scintillation effects on satellite signals. Geomagnetic data from the Greenland ground stations revealed intense local geomagnetic disturbances, likely associated with enhanced Hall currents driven by the upward field-aligned currents linked to the space hurricane. In situ plasma observations from the DMSP and SWARM satellites revealed pronounced electron density enhancements and steep gradients on the morning side of the space hurricane, likely driven by ionospheric convection and soft particle precipitation. This study provides the first comprehensive insight into the space weather effects of space hurricanes.

DOI： 10.1029/2025SW004435

A Bootstrapping Convolutional Neural Network Technique for Optimizing Automated Detection of Equatorial Plasma Bubbles by Optical All-Sky Imagers Reviewed Open Access

Okoh D., Cesaroni C., Rabiu B., Shiokawa K., Otsuka Y., Ogunjo S., Akerele A., Habarulema J.B., Nava B., Migoya-Orué Y., Jamjareegulgarn P., Seun A., Adama O., Ochieng G., Ameh J., Awuor A., Baki P.

Earth and Space Science Vol. 12 ( 6 ) 2025.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Earth and Space Science

Equatorial plasma bubbles (EPBs) disrupt satellite-based communication and navigation systems, particularly in equatorial regions. Reliable detection and classification of EPBs from all-sky imager (ASI) images are essential for accurate space weather monitoring and forecasting. This study presents a novel bootstrapping convolutional neural network (CNN) approach to optimize automated EPB detection on ASI images for operational space weather monitoring applications, and overcoming challenges related to image variability and imbalanced data sets. Data used for CNN training were obtained from the optical mesosphere thermosphere imagers ASI installed at the Space Environment Research Laboratory, National Space Research and Development Agency, Abuja during the period from 2015 to 2020. Our method involved training three sub-models, and aggregating their predictions. The CNN trainings were conducted on three sub-datasets of 3,000 images each, categorized as “EPB,” “Noisy/Cloudy” or “No EPB.” Three corresponding sub-models were developed from the CNN trainings. The three sub-model classifications independently gave prediction accuracies of 98.67%, 98.33%, and 95.83% on a reserved test data set of 600 images. Ensemble models further improved the model prediction accuracies to 99.17% and 99.33% for methods based on the mean of sub-model probabilities and the mode of sub-model classifications respectively. Our results indicate that the bootstrapping CNN technique enhanced the EPB detection accuracy, providing a powerful tool for real-time space weather monitoring applications, and implications for improving operational reliability of satellite-based navigation and communication in the equatorial region.

DOI： 10.1029/2024EA004117

Simultaneous ground-satellite observations of ELF/VLF emissions generated by a strong magnetospheric compression Reviewed Open Access

Claudia Martinez-Calderon, Kazuo Shiokawa, Ondřej Santolík, Satoshi Kurita, Kunihiro Keika, Martin Connors, Ian Schofield, Miroslav Hanzelka, William S. Kurth

Earth, Planets and Space Vol. 77 ( 1 ) 2025.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

We report, for the first time, simultaneous nightside observations of very low frequency waves associated with a strong sudden impulse and subsequent magnetospheric compression. On 23 December 2014 at 11:15 UT we observed an intense sudden impulse characterized by an increase of SYM-H amplitude (~ 63 nT), solar wind speed (300–420 km/s), and dynamic pressure (2–6 nPa) with northwards interplanetary magnetic field. Two minutes later, the sub-auroral receiver at Athabasca (ATH, 54.7ºN, 246.7ºE, L = 4.3) detected a chorus-like burst centered at ~ 2.2 kHz from 11:17 to 11:20 UT (03 MLT). At the same time, the nearby Van Allen Probes B (RBSP-B) spacecraft, also in the pre-midnight sector, detected an emission with the same temporal and frequency variations suggesting a conjugate event. One minute before this wave burst, RBSP-B also observed hiss below 1.5 kHz, which was not detected at ATH. Magnetospheric compression can lead to betatron acceleration of plasmasheet electrons and enhancement of temperature anisotropy regulating electron cyclotron instability and whistler-mode generation. However, our observations suggest the generation mechanism between hiss and the discrete emissions differed at the beginning of the compression, in addition to them having different propagation to the ground. The decrease of magnetic curvature in the equatorial plane, caused by strong magnetospheric compression, could be responsible for the hiss being observed first. The subsequent stretching of the field lines, increasing the curvature, likely contributed to the generation of the discrete emissions. This discrete emission with mostly oblique wave angles propagated unducted to the ground, while the more field-aligned hiss did not. These results indicate detailed characteristics of the temporal development of hiss/chorus-like wave generation and propagation in response to the global magnetosphere compression associated with a solar wind pressure pulse.

Graphical Abstract

DOI： 10.1186/s40623-025-02170-4

Determination of electron heat flux in the topside ionosphere and its impact on the vertical profile of OI 630.0 nm emission rate during nighttime SAR arcs for different solar activity conditions Reviewed

Other Link： https://link.springer.com/article/10.1186/s40623-025-02170-4/fulltext.html

Upadhyay K., Shiokawa K., Pallamraju D., Gololobov A.

Advances in Space Research Vol. 75 ( 6 ) page： 4731 - 4739 2025.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Advances in Space Research

Electron heat flux in the ionosphere plays a crucial role in altering the electron temperature and thermal balance of the electron population, especially over subauroral- and high-latitudes. The downward flow of electron heat flux in the subauroral-latitude ionosphere through magnetosphere-ionosphere coupling causes an enhancement in the electron temperature, thereby leading to the formation of Stable Auroral Red (SAR) arcs. Understanding the relationship between heat flux and electron temperature is critical, as no technique exists to measure heat flux directly in the SAR arc region. This study primarily reports the characteristics of thermal electron heat flux of SAR arcs in the sub-auroral ionosphere and its influence on the plasma densities in the inner-magnetosphere and the SAR arc peak emission altitude. The downward electron heat flux has been characterized by using measured atomic oxygen red line emission intensity in conjunction with simultaneous enhancements of electron temperature by in-situ measurements for several nighttime SAR arc events reported in the literature for the period of 2012–2020 of solar cycle-24, and by using GLOW, a physics-based model. The present investigation reveals considerable variation in the estimated heat flux and SAR arc emission altitudes due to the influence of solar activity. This study, thus, quantifies the electron heat flux, averaging 2.89 × 1011 eV-cm−2-sec-1 near solar minimum and 8.05 × 1012 eV-cm−2-sec-1 during solar maximum, associated with ionospheric heating during observations of nighttime SAR arcs and their relevance to space weather phenomena.

DOI： 10.1016/j.asr.2024.12.046

Automatic Detection of Equatorial Plasma Bubbles in Airglow Images Using Two-Dimensional Principal Component Analysis and Explainable Artificial Intelligence Reviewed Open Access

Yacoub M., Abdelwahab M., Shiokawa K., Mahrous A.

Machine Learning and Knowledge Extraction Vol. 7 ( 1 ) 2025.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Machine Learning and Knowledge Extraction

Equatorial plasma bubbles (EPBs) are regions of depleted electron density that form in the Earth’s ionosphere due to Rayleigh–Taylor instability. These bubbles can cause signal scintillation, leading to signal loss and errors in position calculations. EPBs can be detected in images captured by All-Sky Imager (ASI) systems. This study proposes a low-cost automatic detection method for EPBs in ASI data that can be used for both real-time detection and classification purposes. This method utilizes Two-Dimensional Principal Component Analysis (2DPCA) with Recursive Feature Elimination (RFE), in conjunction with a Random Forest machine learning model, to create an Explainable Artificial Intelligence (XAI) model capable of extracting image features to automatically detect EPBs with the lowest possible dimensionality. This led to having a small-sized and extremely fast-trained model that could be used to identify EPBs within the captured ASI images. A set of 2458 images, classified into two categories—Event and Empty—were used to build the database. This database was randomly split into two subsets: a training dataset (80%) and a testing dataset (20%). The produced XAI model demonstrated slightly higher detection accuracy compared to the standard 2DPCA model while being significantly smaller in size. Furthermore, the proposed model’s performance has been evaluated and compared with other deep learning baseline models (ResNet18, Inception-V3, VGG16, and VGG19) in the same environment.

DOI： 10.3390/make7010026

Responses of the Daytime Low and Equatorial Ionosphere and Thermosphere Over the Indian Region During the Geomagnetic Storm of April 2023 Reviewed

Krishnan L.G., Shiokawa K., Pant T.K., Lu G., Shreedevi P.R., Otsuka Y., Sunda S.

Journal of Geophysical Research Space Physics Vol. 130 ( 3 ) 2025.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

Study of the response of Thermosphere–Ionosphere (TI) system over the Indian longitude sector during the geomagnetic storm of April 23–24, 2023, is presented. The ionosonde observations at the dip equatorial station, Trivandrum (8.52°N, 77°E, dip lat. = 1.96°N), are found to have unusually high F2 peak plasma density (foF2), with three maxima during the daytime on April 24. The Total Electron Content (TEC) observations from different latitudes showed enhancements temporally progressing from north to south. These features are identified as Traveling Ionospheric Disturbances (TIDs) with speeds ∼400 to 750 m/s. Two major enhancements in TEC observed over Trivandrum were concurrent to the first and third maxima in foF2. Simulations of meridional wind and temperature for this storm were carried out using the Thermosphere–Ionosphere–Electrodynamics General Circulation Model (TIEGCM) that was driven with high-latitude inputs derived from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique. Simulations show the signatures of Traveling Atmospheric Disturbances (TADs) in ionospheric F-region, which conform with the TID observations. The second foF2 peak is found to be simultaneous to the modulation in Prompt Penetration Electric Field (PPEF), which is also observed in the drift of the E-region ionospheric plasma irregularities using an HF radar and the Equatorial Electrojet (EEJ) strength measured by ground-based magnetometer. Simultaneously increasing electric field and foF2 implies the presence of storm-time equatorward wind, inhibiting the plasma fountain. This is the first report comparing comprehensive observations and AMIE-TIEGCM modeling studies of daytime responses of low and equatorial TI during a geomagnetic storm.

DOI： 10.1029/2024JA033141

Properties of EMIC Waves and EMIC Wave-Driven Electron Precipitation in Subauroral Latitudes Observed at Athabasca, Canada Reviewed

Asuka Hirai, Fuminori Tsuchiya, Takahiro Obara, Yoshizumi Miyoshi, Yuto Katoh, Yasumasa Kasaba, Kazuo Shiokawa, Atsushi Kumamoto, Yoshiya Kasahara, Shoya Matsuda, Hiroaki Misawa, Satoshi Kurita, Chae-Woo Jun, Hiroyo Ohya, Martin G. Connors

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 130 ( 3 ) 2025.3

Statistical Analysis of Van Allen Probes-B Observations of Stable Auroral Red Arc Intervals in the Overlap Region Between the Plasmasphere and the Ring Current Reviewed Open Access

Sugimura R., Shiokawa K., Miyoshi Y., Smith C., Spence H., Reeves G.

Journal of Geophysical Research Space Physics Vol. 130 ( 3 ) 2025.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

In Earth's inner magnetosphere low-energy-density plasma in the plasmasphere (PS) partially overlaps with higher-energy plasma in the ring current (RC). Auroral emissions with zonally elongated arc-like shapes called Stable Auroral Red (SAR) arcs occur in the subauroral latitudes that are connected to the inner magnetosphere. There has yet to be a statistical analysis of the PS-RC overlap region in which SAR arcs occur. We conducted a statistical analysis of the occurrence characteristics of this PS-RC overlap region for SAR arcs, using the RBSP-B satellite over a 4-year period from 1 January 2015 to 31 December 2018. We defined the PS-RC overlap region based on ground-satellite conjugate observations of SAR arcs on the same geomagnetic field line. The overlap region in which SAR arcs develop is located at pre-midnight for high-energy oxygen ions and post-midnight for low-energy hydrogen ions. Superposed epoch analysis using the SYM-H index shows that the PS-RC overlap occurs near the end of the main phase of magnetic storms for both H+ and O+ ions, indicating that the SAR arc source develops at the particle injection during the end of the storm's main phase. Superposed epoch analysis using the SML index revealed that several substorms occurred near the onset time of the SAR arc source for both ion species. This suggests that particle injection by substorms at the end of the magnetic storm is important for the formation of the SAR arc source.

DOI： 10.1029/2024JA032893

Multi‐Event Analysis of STEVE, SAR Arc, and Red/Green Arc at Subauroral Latitudes Using Data From Ground Optical and Radio Instruments and the Arase and Van Allen Probes Satellites Reviewed Open Access

Rei Sugimura, Kazuo Shiokawa, Yuichi Otsuka, Shin‐ichiro Oyama, Arto Oksanen, Martin Connors, Akira Kadokura, Igor Poddelsky, Nozomu Nishitani, Simon G. Shepherd, J. Michael Ruohoniemi, Charles Smith, Harlan Spence, Geoff Reeves, Herbert O. Funsten, Yoshizumi Miyoshi, Iku Shinohara, Yoshiya Kasahara, Fuminori Tsuchiya, Atsushi Kumamoto, Atsuki Shinbori, Kazushi Asamura, Shoichiro Yokota, Yoichi Kazama, C.‐W. Jun, Shiang‐Yu Wang, Sunny W. Y. Tam, Tzu‐Fang Chang, Bo‐Jhou Wang, Satoshi Kasahara, Kunihiro Keika, Tomoaki Hori, Ayako Matsuoka

Journal of Geophysical Research: Space Physics Vol. 130 ( 2 ) 2025.2

Language：English Publishing type：Research paper (scientific journal) Publisher：American Geophysical Union (AGU)

Abstract

Strong Thermal Emission Velocity Enhancement (STEVE) is a latitudinally narrow, purple‐band emission observed at subauroral latitudes. Stable Auroral Red (SAR) arcs characterized by major red emission, and red/green arcs with both red and green emissions also occur at subauroral latitudes. Characteristics of magnetospheric source plasma and electromagnetic fields of these three types of arcs have not been fully understood because of the limited conjugate observations between magnetosphere and the ground. In this study, we report 11 conjugate observations (2 STEVEs, 7 SAR arcs, and 2 red/green arcs), using all‐sky images obtained at seven ground stations over more than four years from January 2017 to April 2021 and magnetospheric satellites (Arase and Van Allen Probes). We found that, in the inner magnetosphere, the source region of STEVEs and red/green arcs were located outside the plasmasphere, and that of the SAR arc was in the region of spatial overlap between the plasmasphere and ring current region. Electromagnetic waves at frequencies below 1 Hz were observed for STEVEs and red/green arcs. SuperDARN radar data showed a strong westward plasma flow in the ionosphere, especially during STEVE events, whereas the plasma flows associated with SAR arcs and red/green arcs were generally weaker and variable. The STEVE and SAR arc can appear simultaneously at slightly different latitudes and STEVEs and red/green arcs can transform into SAR arcs. These first comprehensive ground‐satellite measurements of three types of subauroral‐latitude auroras increase our understanding on similarlity, differences, and coupling of these auroras in the ionosphere and the magnetosphere.

DOI： 10.1029/2024ja032793

Estimating the drift velocity of plasma bubbles in airglow images using the scale invariant feature transform and the speeded up robust feature algorithms Reviewed

Yacoub M., Abdelwahab M., Shiokawa K., Mahrous A.

Advances in Space Research Vol. 75 ( 2 ) page： 2391 - 2402 2025.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Advances in Space Research

Equatorial plasma bubbles (EPBs) are ionospheric irregularities that can significantly impact radio communication, causing signal scintillation that leads to signal loss and error in position calculations. In this study, we introduced a new technique to estimate the eastward and northward drift velocities of the EPB from ASI data by tracking the Scale Invariant Feature Transform (SIFT) and the Speeded Up Robust Features (SURF) points. The technique has been tested by studying multiple EPBs events detected over the Brazilian sector during the autumn equinox, spring equinox and summer solstice. The chosen events occurred during quiet nights (Kp index ≤ 3) and were observable through two All-Sky imager (ASI) stations. Moreover, the study shows the performance of the technique under different circumstances. It achieves optimal performance on clear-sky nights; however, cloud presence within the ASI field of view increases the error within the estimated values. The estimated velocities were found to be within the range reported by previous studies in the Brazilian sector.

DOI： 10.1016/j.asr.2024.09.071

Signatures of the Long Duration Prompt Penetration Electric Field in the 18 MHz HF Radar Observations Over Thumba Reviewed

Krishnan L.G., Shiokawa K., Pant T.K., Vichare G.

Journal of Geophysical Research Space Physics Vol. 130 ( 1 ) 2025.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

One of the best proxies to estimate the daytime ionospheric zonal electric field from the dynamo region is by probing the drift of the plasma irregularities in the ionospheric E-region by coherent radars, although there have not been many at HF frequencies. The present study is based on the observations of the anomalous variability in the zonal drift of 8.3 m scale size plasma irregularities in the ionospheric E-region during the daytime on 12 October 2021, and 28 November 2022, as observed by an 18 MHz HF radar at Thumba (8.5°N, 77°E, and dip lat. = 1.96°N). The wind perturbations from the lower atmosphere and the electric field penetrating from the solar wind, can both cause the perturbations in the E-region electric field. Based on a comparison with the predicted Prompt Penetration Equatorial Electric Field (PPEF) as ascribed by Manoj et al. (2008, https://doi.org/10.1029/2008ja013381), and the quiet-time dynamo electric field over the longitude of Thumba, we conclude that the perturbations in the electric field on these two events are caused by PPEF mapping to the equatorial region, solely driven by IMF B<inf>Z</inf> oscillations. The former event is a result of a Coronal Mass Ejection, whereas the latter event was caused by a high-speed solar wind associated with coronal hole. The fluctuations in the strength of the Equatorial Electrojet (EEJ) calculated from the magnetic field observations from a pair of equatorial (Tirunelveli) and off-equatorial (Alibag) stations are also found to be well in agreement with the radar observations and modeled PPEF, thereby verifying the E-region observations.

DOI： 10.1029/2024JA033140

Transdisciplinary Network Formation by Institute for Space-Earth Environmental Research, Nagoya University, and Geochemistry Reviewed Open Access

Yasunori Mori, Masayo Minami, Kazuo Shiokawa

Abstracts of Annual Meeting of the Geochemical Society of Japan Vol. 72 ( 0 ) page： 241 2025

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：GEOCHEMICAL SOCIETY OF JAPAN

The Ministry of Education, Culture, Sports, Science and Technology (MEXT)'s "Joint Usage/Collaborative Research System Formation Project: Interdisciplinary Research Area Development Hub Formation Program" aims to accelerate the development of joint research beyond conventional research institutions, communities, and fields, to the expansion into interdisciplinary research areas, and to promote the expansion into interdisciplinary research areas, and to provide opportunities for participation in new interdisciplinary research. Ten universities and research institutes, including the Institute for Materials Research, Tohoku University, were selected for the program in FY2023-2024. In FY2024, "Formation of a Transdisciplinary Network Linking Space Earth Environmental Science with History and Archaeology" with the Institute for Space and Earth Environment Studies (ISEE) at Nagoya University as the core institution was selected. This project aims to create a new interdisciplinary network that integrates space earth environmental science with history and archaeology, to evaluate the impact of severe solar storms on modern civilization, and to champion new developments in history and archaeology through more accurate dating. During the project period (maximum 10 years), the project aims to contribute to the formation of a sustainable developmental society that expands into the universe and to the development of human resources. In promoting this project, ISEE has established the "Office for the Promotion of Transdisciplinary Network" (TranSEHA Director: Masayo Minami). In addition to participating institutions such as the National Museum of Japanese History, Center for Accelerator Mass Spectrometry Laboratory, Yamagata University, Advanced Asian Archaeological Research Center, Kyushu University, Joint Support-Center for Data Science Research, the Institute of Statistical Mathematics, Research Organization of Information and Systems, and Center for Digital Humanities and Social Sciences, Nagoya University, further collaboration with other research institutions and researchers is promoted. We are also promoting further collaboration with other research institutions and researchers. In FY2025, 15 internal and external proposals have been adopted, and these efforts are being vigorously pursued in Japan and abroad. TranSEHA has organized projects that contribute to the formation of interdisciplinary networks, such as the Kick-off Workshop (ISEE, February 2025), JpGU Session (Makuhari, May 2025), and Young Researchers' Seminar (ISEE, July 2025). In FY2025, we plan to continue to promote networking and interdisciplinary research by joint workshops with the Office for the Development of Interdisciplinary Research Strategy, ISEE. In this presentation, we will share the progress of TranSEHA and the future direction of interdisciplinary research, including geochemistry, to contribute to the formation and promotion of a transdisciplinary network.

DOI： 10.14862/geochemproc.72.0_241

Seasonal variations of mesoscale perturbations of OH and O2 rotational temperature in Rikubetsu, Shigaraki and Sata Reviewed

Gavrilov N.M., Koval A.V., Popov A.A., Shiokawa K.

Advances in Space Research 2025

Language：English Publishing type：Research paper (scientific journal) Publisher：Advances in Space Research

The method of digital difference filters has been applied to the analysis of OH and O<inf>2</inf> rotational temperature obtained with airglow temperature photometers installed at Rikubetsu (43.5°N, 143.8°E), Shigaraki (34.8°N, 136.1°E), and Sata (31.0°N, 130.7°E) in Japan. These nightglow observations cover the time interval of 2010–2018 at altitudes between 85 and 90 km. Seasonal variations in the monthly standard deviation of rotational temperature perturbations with periods of 0.7–8 h, which may be partly associated with internal gravity waves (IGWs) in the mesopause region, have been studied. Near the mesopause, seasonal variations in the relative standard deviation of the rotational temperature have maxima, the strength and timing of which depend on the location of the observing site and on the type of nighttime emission. These differences can be caused by differences in the activity of wave sources and conditions of wave propagation, differences in heights of different emission layers and seasonal changes in the complex system of photochemical processes for OH and O<inf>2</inf> nightglows.

DOI： 10.1016/j.asr.2025.06.023

Post-midnight purple arc and patches appeared on the high latitude part of the auroral oval: Dawnside counterpart of STEVE? Reviewed Open Access

Sota Nanjo, Gabriel Arne Hofstra, Kazuo Shiokawa, Atsuki Shinbori, Satonori Nozawa, Keisuke Hosokawa

Earth, Planets and Space Vol. 76 ( 1 ) 2024.12

Spatial structures of blue low-latitude aurora observed from Japan during the extreme geomagnetic storm of May 2024 Reviewed Open Access

Nanjo S., Shiokawa K.

Earth Planets and Space Vol. 76 ( 1 ) 2024.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Earth Planets and Space

On May 11, 2024, an extreme G5-class geomagnetic storm triggered a spectacular and unusual display of colorful auroras in mid- to low-latitude regions all over the world. In Japan, auroras were seen not only from Hokkaido, the northernmost island, but also from the northern and central parts of Honshu, the main island. The widespread availability of commercial digital cameras among the public led to a flooding of high-resolution auroral images on social media. This study reports on the appearance of a blue-dominant aurora during a storm-time substorm on this day and its magnetic field-aligned and longitudinal structures captured by citizen scientists. Observations from two photographers at different locations revealed that the aurora was located at approximately 40 degrees magnetic latitude and magnetic local time (MLT) of 23 h, spanned about 1200 km (1-h MLT) in the longitudinal direction with three separated structures, and ranged in altitude from 400 km to at least 900 km. Simultaneous photometric measurements suggested that this blue-dominant aurora likely included emissions at 427.8 nm. While previous studies have noted the existence of emissions at 427.8 nm in low-latitude auroras, this is the first time that a blue-dominant low-latitude aurora has been spatially identified and shown to have longitudinal and field-aligned structures. Additionally, previous studies suggested that blue emissions in low-latitude auroras are produced by energetic neutral atoms from the ring current. However, identifying longitudinal and field-aligned structures in this study may need an alternative explanation.

DOI： 10.1186/s40623-024-02090-9

Mid-Latitude Auroras and Energetic Particle Precipitation Occurred Unusually in a Moderate Magnetic Storm on 1 December 2023 Reviewed

Properties of EMIC waves and EMIC wave-driven REP observed in subauroral latitudes Reviewed

2024.9

Ma L., Yu Y., Ding X., Liu X., An D., Zhou C., Cao J., Shiokawa K.

Geophysical Research Letters Vol. 51 ( 18 ) 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Geophysical Research Letters

Mid-latitude auroras are conventionally generated during intense magnetic storms. However, mid-latitude auroras were observed by naked eyes at Beijing China (39°N, 116°E) unusually during a moderate storm event on 1 December 2023 with the minimum Sym-H index only (Formula presented.) −120 nT. This study combines conjugative in-site and ground-based observations to analyze the auroras and underlying physical processes. Results indicate that both electron and proton auroras appeared at low latitudes. Electron auroras predominantly arise from low-energy electron precipitation, but proton auroras may be explained by energetic tens of keV proton precipitation. Pc1/EMIC waves are observed at low latitudes in the ionosphere, potentially accounting for mid-latitude proton auroras. Downward field-aligned currents (FACs) are also detected at low latitudes, producing significant magnetic perturbations. This study reveals the underlying ionospheric responses to the mid-latitude auroras to understand potential reasons for observing aurora at such mid-latitudes during a moderate storm.

DOI： 10.1029/2024GL110764

Precipitation of Auroral Electrons Accelerated at Very High Altitudes: Impact on the Ionosphere and a Possible Acceleration Mechanism Reviewed Open Access

S. Imajo, Y. Miyoshi, Y. Kazama, K. Asamura, I. Shinohara, K. Shiokawa, Y. Kasahara, Y. Kasaba, A. Matsuoka, S.‐Y. Wang, S. W. Y. Tam, T.‐F. Chang, B.‐J. Wang, C.‐W. Jun, M. Teramoto, S. Kurita, F. Tsuchiya, A. Kumamoto, K. Saito, T. Hori

Journal of Geophysical Research: Space Physics Vol. 129 ( 9 ) 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：American Geophysical Union (AGU)

Abstract

The Arase satellite observed the precipitation of monoenergetic electrons accelerated from a very high altitude above 32,000 km altitude on 16 September 2017. The event was selected in the period when the high‐angular resolution channel of the electron detector looked at pitch angles within ∼5° from the ambient magnetic field direction, and thereby was the first to examine the detailed distribution of electron flux near the energy‐dependent loss cone at such high altitudes. The potential energy below the satellite estimated from the observed energy‐dependence of the loss cone was consistent with the energy of the upgoing ion beams, indicating that ionospheric ions were accelerated by a lower‐altitude acceleration region. The accelerated electrons inside the loss cone carried a significant net field‐aligned current (FAC) density corresponding to ionospheric‐altitude FAC of up to ∼3μA/m2. Based on the anisotropy of the accelerated electrons, we estimated the height of the upper boundary of the acceleration region to be >∼2 RE above the satellite. The height distribution of the acceleration region below the satellite, estimated from the frequency of auroral kilometric radiation, was ∼4,000–13,000 km altitude, suggesting that the very‐high‐altitude acceleration region was separated from the lower acceleration region. Additionally, we observed time domain structure (TDS) electric fields on a subsecond time scale with a thin FAC indicated by magnetic deflections. Such a TDS may be generated by the formation of double layers in the magnetotail, and its potential drop could significantly contribute (∼40%–60%) to the parallel energization of precipitating auroral electrons.

DOI： 10.1029/2024ja032696

First Observation of Temporal Variation of STEVE Altitudes Using Triangulation by Two Color Cameras Reviewed Open Access

Chen L., Shiokawa K., Connors M., Kato Y., Tsuboi T.

Journal of Geophysical Research Space Physics Vol. 129 ( 9 ) 2024.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

We present a unique triangulation measurement of Strong Thermal Emission Velocity Enhancement (STEVE) observed on Sept 3rd, 2022, at Athabasca, Canada. Using two Digital single-lens reflex (DSLR) color cameras with all-sky fish-eye lenses, we show the profile of STEVE altitude variation over time in 1 min resolution for the first time. We estimate the altitude variation of its visible purplish arc and green picket fence structures. We also compare the DLSR camera images with narrowband all-sky images of an Optical Mesosphere Thermosphere Imager (OMTI) to see the correspondence of color camera images with 630 nm and OH-band auroral/airglow emission images. The height of the purplish STEVE arc was stable at 150–170 km while present (∼0,546–0,633 UT), except for a short excursion to ∼200 km at 0,600 UT. The green picket fence structures appeared at 0,549 UT when the intensity of the STEVE arc started to intensify. They presented only for ∼7 min, and their altitude was steady at ∼110 km. The vertical movement of the STEVE arc to ∼200 km was found to be accompanied by the motion across the local magnetic field lines, suggesting a southward E × B drift underlying the westward ion drift. From the comparison with the OMTI images, we find that the purplish STEVE arc moved closer to the 630 nm arc in the all-sky image when it rose to a higher altitude, indicating the occurrence of electron heating at a same or slightly higher altitude than the STEVE.

DOI： 10.1029/2024JA032436

Search for Pulsed Ultralow-Frequency Electromagnetic Precursors of Earthquakes Reviewed

Martines-Bedenko V.A., Pilipenko V.A., Shiokawa K., Kasimova V.A.

Izvestiya Physics of the Solid Earth Vol. 60 ( 4 ) page： 726 - 735 2024.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Izvestiya Physics of the Solid Earth

Abstract—Numerous publications have appeared in the literature describing a new seismo-electromagnetic effect—the appearance of magnetic pulses with a duration of 1–40 s, which are detected at distances up to ten thousand km a few minutes before earthquakes of even low magnitude. An assumption was made about the universality of the processes responsible for generation of pulsed precursors and the fundamental possibility of a short-term (a few minutes) warning of an approaching earthquake. In this article, the possibility of the occurrence of ultra-low-frequency pulses that precede seismic events with magnitudes M > 5.0 is studied based on the data from a network of induction magnetometers in the Far East. Pulsed disturbances occur regularly in the records by these highly sensitive magnetometers. Some pulses are observed synchronously at several stations, which excludes their origin from local noise. The spectral maximum of about 7–8 Hz of the oscillatory structure, which appears in many pulses, corresponds to the fundamental frequency of the Schumann resonator. A comparison of magnetic observations with data from the World Wide Lightning Location Network (WWLLN) showed that some of the pulses were caused by lightning discharges in the 650 km vicinity of magnetic station. Although some of the impulses are observed immediately before earthquakes, their connection with seismic activity cannot be claimed with certainty. The calculation of the number of pulses within the 5-min interval before and after the seismic shock shows that they are randomly distributed around the time of the earthquake. Apparently, the pulses are mainly due to the ionospheric response to a distant lightning discharge.

DOI： 10.1134/S106935132470071X

Comparison of Very Low Frequency Wave Intensities Measured by a Low‐Altitude Spacecraft and on the Ground Reviewed Open Access

F. Němec, K. Drastichová, J. Manninen, C. Martinez‐Calderon, K. Shiokawa, M. Connors

Journal of Geophysical Research: Space Physics Vol. 129 ( 7 ) 2024.7

Language：English Publishing type：Research paper (scientific journal) Publisher：American Geophysical Union (AGU)

Abstract

We evaluate average wave intensities at frequencies up to 10 kHz measured by two ground stations in Canada and two others in Finland at auroral and subauroral latitudes over a full year, as well as by the low‐altitude DEMETER spacecraft during the years 2004–2010. Lightning location and energy data obtained by the World Wide Lightning Location Network, along with geomagnetic activity characterized by the Kp index, are further used. Latitudinal, diurnal, and annual variations are analyzed, and the global intensities measured on the ground and by the spacecraft are systematically compared for the first time. We show that lightning‐generated waves often dominate the measured wave intensities, particularly during the night, in summer, and at higher frequencies. DEMETER observations, supported by ray‐tracing analysis, reveal a significant role of nonducted lightning‐generated whistler propagation between the hemispheres. Finally, the wave intensity response to geomagnetic activity variations is quite different on the ground compared to in space. While spacecraft‐measured wave intensities are considerably larger during periods of enhanced geomagnetic activity, the ground‐based intensities are only sporadically enhanced during geomagnetically active periods.

DOI： 10.1029/2024ja032655

Occurrence of Mesospheric Frontal Structures Over the High Latitude Station, Tromsø, Norway Reviewed

Chauhan N., Shiokawa K., Gurubaran S., Nozawa S., Oyama S.i., Nakamura T.

Journal of Geophysical Research Space Physics Vol. 129 ( 7 ) 2024.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

Observational data sets for the high latitude middle atmosphere are key to understand the dynamics over those latitudes and the coupling between the lower and middle atmosphere. Utilizing long-term data sets from an all-sky imager at Tromsø, Norway (69.6°N, 19.2°E), the characteristics of 18 mesospheric frontal events in the Arctic winter mesosphere from 2011 to 2015 were studied. These frontal events exhibit horizontal extensions exceeding 500 km and were characterized by a sharp leading front, sometimes followed by a quasi-monochromatic wave train or a turbulent region. A subset of these frontal gravity wave events has been identified in the past as “bores.” While there have been numerous previous reports from low- and mid-latitude sites, and also from southern high latitudes, there have been a few from northern high latitudes. This study focuses on the frontal events in the northern high latitudes and provides new insights into the characteristics of these events. Their horizontal wavelengths primarily ranged from 20 to 40 km, and they exhibited phase speeds in the range 30–80 m/s. Most events were observed before local midnight. No clear link between these events and auroral activity was found. The majority of fronts were found propagating in the north-west direction, which might be due to the wind filtering effects.

DOI： 10.1029/2023JA032243

Spatiotemporal development of cosmic noise absorption at subauroral latitudes using multipoint ground‐based riometers Reviewed

Kato, Y, Shiokawa, K, Tanaka, Y, Ozaki, M, Kadokura, A, Oyama, S.‐i, Alexey Oinats, Martin Connors, Dmitry Baishev

Journal of Geophysical Research: Space Physics Vol. 129 ( 7 ) 2024.7

Magnetic Storm-Time Red Aurora as Seen From Hokkaido, Japan on 1 December 2023 Associated With High-Density Solar Wind Reviewed Open Access

Ryuho Kataoka, Yoshizumi Miyoshi, Kazuo Shiokawa, Nozomu Nishitani, Kunihiro Keika, Takanobu Amano, Kanako Seki

Geophysical Research Letters Vol. 51 ( 12 ) 2024.6

Special issue of SCOSTEP's 15th Quadrennial Solar-Terrestrial Physics Symposium (STP-15) Reviewed Open Access

Shiokawa K., Marsh D., Pallamraju D., Patsourakos S., Pedatella N., Ratnam M.V., Rozanov E., Srivastava N., Tulasiram S.

Journal of Atmospheric and Solar Terrestrial Physics Vol. 259 2024.6

Global Distribution of EMIC Waves and Its Association to Subauroral Proton Precipitation During the 27 May 2017 Storm: Modeling and Multipoint Observations Reviewed

P. R. Shreedevi, Yiqun Yu, Yoshizumi Miyoshi, Xingbin Tian, Minghui Zhu, Vania K. Jordanova, Satoko Nakamura, Chae‐Woo Jun, Sandeep Kumar, Kazuo Shiokawa, Martin Connors, T. Hori, Masafumi Shoji, I. Shinohara, S. Yokota, S. Kasahara, K. Keika, A. Matsuoka, Akira Kadokura, Fuminori Tsuchiya, Atsushi Kumamoto, Yoshiya Kasahara

Journal of Geophysical Research: Space Physics Vol. 129 ( 6 ) 2024.5

Language：English Publishing type：Research paper (scientific journal) Publisher：American Geophysical Union (AGU)

Abstract

Recent simulation studies using the RAM‐SCB model showed that proton precipitation contributes significantly to the total energy flux deposited into the subauroral ionosphere thereby affecting the magnetosphere‐ionosphere coupling. In this study, we use the BATS‐R‐US + RAM‐SCB model to understand the evolution of ElectroMagnetic Ion Cyclotron (EMIC) waves in the inner magnetosphere, their correspondence to the proton precipitation into the subauroral ionosphere, and to assess the performance of the model in reproducing the EMIC wave‐particle interactions. During the 27 May 2017 storm, Arase and RBSP‐A satellites observed typical signatures of EMIC waves in the inner magnetosphere. Within this interval, Defense Meteorological Satellite Program (DMSP) and National Oceanic and Atmospheric Administration (NOAA)/MetOp satellites observed significant proton precipitation in the dusk‐midnight sector. Simulation results show that H‐ and He‐band EMIC waves are excited within regions of strong temperature anisotropy near the plasmapause. The simulated growth rates of EMIC waves show a similar trend to that of the EMIC wave power observed by the Arase and RBSP‐A satellites, suggesting that the model can reproduce the EMIC wave activity qualitatively. The simulated H‐band waves in the dusk sector are stronger than He‐band waves possibly due to the presence of excess protons in the boundary conditions obtained from the BATS‐R‐US code. The precipitating proton fluxes reproduced by the simulation with EMIC waves are found to agree reasonably well with the DMSP and NOAA/MetOp satellite observations. It is suggested that EMIC wave scattering of ring current ions can account for proton precipitation observed by the DMSP and MetOp satellites during the 27 May 2017 storm.

DOI： 10.1029/2023ja032337

Observation and Numerical Simulation of Cold Ions Energized by EMIC Waves Reviewed Open Access

K.‐H. Kim, C.‐W. Jun, J.‐W. Kwon, J. Lee, K. Shiokawa, Y. Miyoshi, E.‐H. Kim, K. Min, J. Seough, K. Asamura, I. Shinohara, A. Matsuoka, S. Yokota, Y. Kasahara, S. Kasahara, T. Hori, K. Keika, A. Kumamoto, F. Tsuchiya

Journal of Geophysical Research: Space Physics Vol. 129 ( 5 ) 2024.5

Language：English Publishing type：Research paper (scientific journal) Publisher：American Geophysical Union (AGU)

Abstract

This is the first report of significant energization (up to 7,000 eV) of low‐energy He+ ions, which occurred simultaneously with H‐band electromagnetic ion cyclotron (EMIC) wave activity, in a direction mostly perpendicular to the ambient magnetic field. The event was detected by the Arase satellite in the dayside plasmatrough region off the magnetic equator on 15 May 2019. The peak energy of the He+ flux enhancements is mostly above 1,000 eV. At some interval, the He+ ions are energized up to ∼7,000 eV. The H‐band waves are excited in a frequency band between the local crossover and helium gyrofrequencies and are close to a linear polarization state with weakly left‐handed or right‐handed polarization. The normal angle of the waves exhibits significant variation between 0° and 80°, indicating a non‐parallel propagation. We run a hybrid code with parameters estimated from the Arase observations to examine the He+ energization. The simulations show that cold He+ ions are energized up to more than 1,000 eV, similar to the spacecraft observations. From the analysis of the simulated wave fields and cold plasma motions, we found that the ratio of the wave frequency to He+ gyrofrequency is a primary factor for transverse energization of cold He+ ions. As a consequence of the numerical analysis, we suggest that the significant transverse energization of He+ ions observed by Arase is attributed to H‐band EMIC waves excited near the local helium gyrofrequency.

DOI： 10.1029/2023ja032361

Westward Excursion of Pc1/EMIC Waves and Their Source Protons: Paradoxical Observations From Ground and Space Reviewed

Yin Z.F., Zhou X.Z., Hu Z.J., Yue C., Zong Q.G., Liu Z.Y., Liu J.J., Shiokawa K., Oyama S.i., Baishev D.

Journal of Geophysical Research Space Physics Vol. 129 ( 5 ) 2024.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

Pc1 geomagnetic pulsations within the frequency range of 0.2–5 Hz, the ground signatures of electromagnetic ion cyclotron (EMIC) waves, are usually observed to progress westward. A plausible explanation is that their westward-excursion speed is defined by the drift velocity of the source particles in the geomagnetic dipole field. In this study, this relationship is examined through conjugate observations from ground-based and spaceborne instruments. The ground-based observations, including Pc1 pulsations and auroral emissions, consistently demonstrate a westward-excursion speed of ∼4–5 MLT per hour, which agrees with the time delay between EMIC wave observations at two equatorial spacecraft. Observations of the wave source particles, however, indicate an inconsistency between the slow westward excursion speed and the high energy of the wave source protons. This apparent inconsistency is reconciled by the trapping motion of energetic particles within magnetic dips, which is supported by the simultaneous flux enhancements of protons across a broad energy range between ∼50 and ∼100 keV. These results improve our understanding of the westward excursion of Pc1 pulsations, and also underscore the need for caution when directly linking their westward-excursion speed to the energies of the source particles.

DOI： 10.1029/2023JA032317

Statistical Analysis of Low-Latitude Boundary of Polar-Type Medium-Scale Traveling Ionospheric Disturbances Observed by a 630-nm Airglow Imager at Nyrölä, Finland Reviewed Open Access

Masaki Sato, Kazuo Shiokawa, Shin ichiro Oyama, Yuichi Otsuka, Atsuki Shinbori, Arto Oksanen

Journal of Geophysical Research: Space Physics Vol. 129 ( 4 ) 2024.4

New observational projects in New Zealand for studying radiation belt loss processes in the deep inner magnetosphere: instrumentation, operation by solar power and initial results Reviewed Open Access

Yuki Obana, Kaori Sakaguchi, Masahito Nosé, Keisuke Hosokawa, Peter Jaquiery, Satoko Saita, Kazuo Shiokawa, Martin Connors, Akira Kadokura, Tsutomu Nagatsuma, Tanja Petersen

Earth, Planets and Space Vol. 76 ( 1 ) 2024.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

This paper describes the instrumentation and the first results of an upper atmospheric observing project conducted in New Zealand. We operate an all-sky aurora camera and a 64-Hz sampling induction magnetometer at Middlemarch, as well as 1-Hz sampling fluxgate magnetometers which have been operative at three stations in New Zealand, Middlemarch, Eyrewell and Te Wharau. Green and red auroras corresponding to the 557.7 nm and 630.0 nm emissions, respectively, were observed on the night of 5 August 2019. Pc1 pulsations were observed in the frequency range of ~ 0.2–1 Hz before and after a small (minimum Dst = − 40 nT) geomagnetic storm during 4–6 October 2020. Before the geomagnetic storm, Pc1 pulsations with several center frequencies were observed regardless of local time. During the recovery phase, an IPDP (interval of pulsations of diminishing period) type of Pc1 and four subsequent intervals of Pc1s were detected. The Ionospheric Alfvén Resonator (IAR) was also identified with spectral resonance structures during this magnetic storm. Lower harmonic modes of the IAR were present throughout the local nighttime, but higher harmonic modes with frequency of 5–15 Hz seemed to disappear at the onset time of substorms. This is the first report of the IAR at such a high frequency range and this is the first IAR observation in the southern hemisphere. Examples of applying cross-phase analysis to observation data of fluxgate magnetometers are also given.

Graphical Abstract

DOI： 10.1186/s40623-024-01990-0

Other Link： https://link.springer.com/article/10.1186/s40623-024-01990-0/fulltext.html

How to identify and forecast severe space weather events Reviewed

Balan N., Zhang Q.H., Ram S.T., Shiokawa K., Manu V., Xing Z.Y.

Journal of Atmospheric and Solar Terrestrial Physics Vol. 256 2024.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Atmospheric and Solar Terrestrial Physics

This paper reviews some of the work performed by the authors over the past decade regarding the identification and forecasting of severe space weather. Severe space weather (SvSW) is defined as those causing damage of ground installations such as transformers resulting in power outage and/or tele-communication networks resulting in communication failure; normal space weather (NSW) does not cause such severe effects. Severe space weather (ScSW) events are caused by very energetic coronal mass ejections (CMEs) from the Sun, in particular by the sharp changes at their leading edge or front. It is shown that (1) it is the ICME (interplanetary CME) front of large velocity jump ΔV by over 275 km s−1 and sufficiently large southward interplanetary magnetic field (IMF Bz) at and beyond the velocity jump that causes SvSW. (2) A derived parameter of the geomagnetic storms called impulsive strength (IpsDst) giving the average value of Dst during the storm main phase (MP) can distinguish between SvSW and NSW. (3) The product of the observed velocity jump and associated IMF Bz southward (ΔVBz) ≤ −15000 km s−1 nT or −15 mV/m) can be used for forecasting SvSW. (4) If one can estimate ΔVBz at the Sun-Earth L1 point based on observations such as from the Advanced Composition Explorer (ACE) satellite, it is possible to forecast an SvSW event with an advance warning time of about half an hour.

DOI： 10.1016/j.jastp.2024.106183

Variation in the Reflection Height of VLF/LF Transmitter Signals in the D‐Region Ionosphere and the Possible Source: A 2018 Meteoroid in Hokkaido, Japan Reviewed

Thermospheric Wind Response to March 2023 Storm: Largest Wind Ever Observed With a Fabry-Perot Interferometer in Tromsø, Norway Since 2009 Reviewed Open Access

S. Oyama, H. Vanhamäki, L. Cai, A. Shinbori, K. Hosokawa, T. Sakanoi, K. Shiokawa, A. Aikio, I. I. Virtanen, Y. Ogawa, Y. Miyoshi, S. Kurita, N. Nishitani

Space Weather Vol. 22 ( 3 ) 2024.3

H. Ohya, T. Suzuki, F. Tsuchiya, H. Nakata, K. Shiokawa

Radio Science Vol. 59 ( 3 ) 2024.2

Language：English Publishing type：Research paper (scientific journal) Publisher：American Geophysical Union (AGU)

Abstract

Several studies have examined ionospheric variation associated with meteorites, meteoroids, or meteors based on Global Satellite Navigation System total electron content observations. However, there have been few quantitative studies of the D‐region of the ionosphere (60–90 km), which is associated with meteoroids. We investigated variation in the D‐region during the passage of a meteoroid over northeastern Hokkaido, Japan, at 11:55:55 UT on 18 October 2018, using very low‐frequency (VLF, 3–30 kHz) and low‐frequency (LF, 30–300 kHz) signals observed by three transmitters [JJY (40 kHz), JJY (60 kHz), and JJI (22.2 kHz)], at Rikubetsu, Japan. Periodic variation of 100–200 s was observed in the VLF and LF amplitudes upon arrival of the acoustic wave. The vertical seismic velocity of Hi‐net and F‐net data also showed acoustic waves. Although the main period of the acoustic wave was 0.1–0.5 s in the seismic data, a longer period component (100–200 s) remained during propagation up to the D‐region ionosphere. The estimated velocity of the acoustic waves was ∼340 m/s on the ground according to the Hi‐net seismic data. The acoustic wave originated near the endpoint (25 km altitude) of the meteoroid trajectory. Based on the observed propagation time of the acoustic waves and ray tracing results, the acoustic waves propagated obliquely from near the endpoint of the meteoroid trajectory up to a D‐region height (about ∼90 km altitude), south of the Rikubetsu receiver.

DOI： 10.1029/2023rs007801

Longitudinal Development of Cosmic Noise Absorption Based on Multipoint Observations at Subauroral Latitudes During Storm‐Time Substorms on 25–28 August 2018 Reviewed Open Access

Yuto Kato, Kazuo Shiokawa, Yoshimasa Tanaka, Mitsunori Ozaki, Akira Kadokura, Shin‐ichiro Oyama, Alexey Oinats, Martin Connors, Dmitry Baishev

Journal of Geophysical Research: Space Physics Vol. 129 ( 1 ) 2024.1

Language：English Publishing type：Research paper (scientific journal) Publisher：American Geophysical Union (AGU)

Abstract

Enhancements in electron density in the D‐region ionosphere attributed to the precipitation of high‐energy electrons, have previously been inferred from increases in cosmic radio noise absorption (CNA) using ground‐based riometers. However, there have been few studies of CNA observations at multi‐point stations distributed in longitudes. Thus, the spatio‐temporal development of the global distribution of CNA is not well understood. In this study, we investigated the longitudinal extent of CNA using simultaneous riometer observations at six stations at subauroral latitudes in Canada, Alaska, Russia, and Iceland. These stations are located encircling the earth at ∼60° north magnetic latitudes. We have conducted simultaneous observations of CNA at these stations since October 2017. Here we focus on seven substorms during a geomagnetic storm 25–28 August 2018 and study the spatio‐temporal development of the global distribution of CNA during these substorms. For all seven substorms, some stations observed CNA enhancements after the substorm onsets. In five cases, the CNA enhancements started around midnight and expanded eastward. The other two cases show westward and anti‐sunward development of CNA. The eastward expansion of CNA indicates the eastward drift of high‐energy electrons, which is the source of the CNA, due to gradient and curvature drift in the geomagnetic field. The westward expansion of CNA may correspond to westward expansion of the substorm injection region due to dawn‐to‐dusk electric fields. These results indicate that spatio‐temporal development of CNA at subauroral latitudes corresponds to high energy electron drift in the inner magnetosphere.

DOI： 10.1029/2023JA031950

A Closer Cooperation between Space and Seismology Communities – a Way to Avoid Errors in Hunting for Earthquake Precursors Reviewed Open Access

Pilipenko V.A., Shiokawa K.

Russian Journal of Earth Sciences Vol. 24 ( 1 ) 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：Russian Journal of Earth Sciences

The space physicists and the earthquake (EQ) prediction community exploit the same instruments – magnetometers, but for different tasks: space physicists try to comprehend the global electrodynamics of near-Earth space on various time scales, whereas the seismic community develops electromagnetic methods of short-term EQ prediction. The lack of deep collaboration between those communities may result sometimes in erroneous conclusions. In this critical review, we demonstrate some incorrect results caused by a neglect of specifics of geomagnetic field evolution during space weather activation. The considered examples comprise: Magnetic storms as a trigger of EQs; ULF waves as a global EQ precursor; Geomagnetic impulses before seismic shocks; Long-period geomagnetic disturbances generated by strong EQs; Discrimination of underground ULF sources by amplitude-phase gradients; Depression of ULF power as a short-term EQ precursor; and Detection of seimogenic emissions by satellites. To verify the reliability of the above widely disseminated results data from available arrays of fluxgate and search-coil magnetometers have been re-analyzed. In all considered events, the “anomalous” geomagnetic field behavior can be explained by global geomagnetic activity, and it is apparently not associated with seismic activity. This critical review does not claim that ULF electromagnetic field cannot be used as a sensitive indicator of the EQ preparation processes, but we suggest that both communities must cooperate their studies more tightly using data exchange, combined usage of magnetometer networks, organization of CDAW for unique events, etc.

DOI： 10.2205/2024ES000899

Pathways to global coordination in space weather: International organizations, initiatives, and space agencies Reviewed

Ishii M., Eduardo Rezende Costa J., Kuznetsova M.M., Andries J., Gopalswamy N., Belehaki A., Alfonsi L., Shiokawa K., Stanislawska I., Bingham S., Kalegaev V., Kent Tobiska W., Rees D., Glover A., Spann J.F.

Advances in Space Research 2024

Language：English Publishing type：Research paper (scientific journal) Publisher：Advances in Space Research

This paper is the second part of two papers on global coordination in space weather. In this paper the activities of established and emerging international organizations and initiatives related to space weather research and operations are introduced. As shown in the accompanying paper “Global Landscape of Space Weather Observations, Research and Operations”, most of instrumentations for space environment monitoring are operated by each country. On the other hand, it is necessary to integrate the global observation to detect space weather phenomena, and it is essential to coordinate among nations for data sharing, set standard formats and protocols, fill observational gaps, etc. There are multiple international organizations and other actors in the field of space weather, and they have their own purposes and goals. In 2022, three international organizations, WMO, ISES and COSPAR reached an agreement to explore pathways to increased coordination of activities. There is also an emerging movement by various space agencies that fund space weather research missions to establish a forum to share plans and foster discussions leading to possible collaborations that advance understanding and enable progress of space weather operations and applications.

DOI： 10.1016/j.asr.2024.06.017

On the Creation, Depletion, and End of Life of Polar Cap Patches Reviewed Open Access

Eriksen, NK; Lorentzen, DA; Oksavik, K; Baddeley, L; Hosokawa, K; Shiokawa, K; Bland, E; Paxton, L; Zhang, YL; Mcwilliams, K; Yeoman, T; Themens, DR

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 128 ( 12 ) 2023.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

Ionospheric convection patterns from the Super Dual Auroral Radar Network are used to determine the trajectories, transit times, and decay rates of three polar cap patches from their creation in the dayside polar cap ionosphere to their end of life on the nightside. The first two polar cap patches were created within 12 min of each other and traveled through the dayside convection throat, before entering the nightside auroral oval after 104 and 92 min, respectively. When the patches approached the nightside auroral oval, an intensification in the poleward auroral boundary occurred close to their exit point, followed by a decrease in the transit velocity. The last patch (patch 3) decayed completely within the polar cap and had a lifetime of only 78 min. After a change in drift direction, patch 3 had a radar backscatter power half-life of 4.23 min, which reduced to 1.80 min after a stagnation, indicating a variable decay rate. 28 minutes after the change in direction, and 16 min after coming to a halt within the Clyde River radar field-of-view, patch 3 appeared to reach its end of life. We relate this rapid decay to increased frictional heating, which speeds up the recombination rate. Therefore, we suggest that the slowed patch motion within the polar cap convection pattern is a major factor in determining whether the patch survives as a recognizable density enhancement by the time the flux tubes comprising the initial patch cross into the nightside auroral oval.

DOI： 10.1029/2023JA031739

Geomagnetic Effect of the Atmospheric Acoustic Resonance Excited by Earthquakes and Volcano Eruptions Reviewed

Surkov, VV; Pilipenko, VA; Shiokawa, K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 128 ( 10 ) 2023.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

An analytical model of the vertical acoustic resonance between the thermosphere and the earth's surface and its geomagnetic effect has been constructed. Resonance with a frequency of several mHz occurs when an atmospheric acoustic wave (AW) is excited by vibrations of the earth or ocean surface. The derived analytical relationships give a possibility to examine the dependence of the fundamental resonant frequency on the height of the reflecting atmospheric layer and horizontal AW number. Geomagnetic disturbances caused by the impact of AW on the ionosphere are calculated within the framework of a multi-layered model of the ground-atmosphere-ionosphere system. The E-layer of the ionosphere is treated in the approximation of a thin layer with an inclined geomagnetic field, while the topside ionosphere is assumed to consist of a cold collisionless plasma. The dependence of the spectral power of magnetic perturbations on the direction of the horizontal AW propagation is examined. The magnetic perturbation spectra are shown to have maxima at frequencies close to the acoustic resonance frequency. The spectral powers of magnetic perturbations and barometric variations measured during the Iwate-Miyagi Nairik earthquake are in accordance with the model predictions for realistic media and AW parameters. Field-aligned currents that arise when AWs enter the ionospheric E-layer is shown to carry measurable electromagnetic disturbances into the geomagnetically conjugated region.

DOI： 10.1029/2023JA031872

Correspondence of Pi2 pulsations, aurora luminosity, and plasma flux fluctuation near a substorm brightening aurora: Arase observations Reviewed

L. Chen, K. Shiokawa, Y. Miyoshi, S. Oyama, C‐W. Jun, Y. Ogawa, K. Hosokawa, Y. Kazama, S. Y. Wang, S. W. Y. Tam, T. F. Chang, B. J. Wang, K. Asamura, S. Kasahara, S. Yokota, T. Hori, K. Keika, Y. Kasaba, A. Kumamoto, F. Tsuchiya, M. Shoji, Y. Kasahara, A. Matsuoka, I. Shinohara, S. Nakamura

Journal of Geophysical Research: Space Physics 2023.9

Language：English Publishing type：Research paper (scientific journal) Publisher：American Geophysical Union (AGU)

Abstract

Although many substorm‐related observations have been made, we still have limited insight into propagation of the plasma and field perturbations in Pi2 frequencies (∼7‐25 mHz) in association with substorm aurora, particularly from the auroral source region in the inner magnetosphere to the ground. In this study, we present conjugate observations of a substorm brightening aurora using an all‐sky camera and an inner‐magnetospheric satellite Arase at L ∼ 5. A camera at Gakona (62.39oN, 214.78oE), Alaska, observed a substorm auroral brightening on December 28, 2018, and the footprint of the satellite was located just equatorward of the aurora. Around the timing of the auroral brightening, the satellite observed a series of quasi‐periodic variations in the electric and magnetic fields and in the energy flux of electrons and ions. We demonstrate that the diamagnetic variations of thermal pressure and medium‐energy ion energy flux in the inner magnetosphere show approximately one‐to‐one correspondence with the oscillations in luminosity of the substorm brightening aurora and high‐latitudinal Pi2 pulsations on the ground. We also found their anti‐correlation with low‐energy electrons. Cavity‐type Pi2 pulsations were observed at mid‐ and low‐latitudinal stations. Based on these observations, we suggest that a wave phenomenon in the substorm auroral source region, like ballooning type instability, play an important role in the development of substorm and related auroral brightening and high‐latitude Pi2, and that the variation of the auroral luminosity was directly driven by keV electrons which were modulated by Alfven waves in the inner magnetosphere.

DOI： 10.1029/2023ja031648

A machine learning approach for total electron content (TEC) prediction over the northern anomaly crest region in Egypt Reviewed Open Access

Rukundo W., Shiokawa K., Elsaid A., AbuElezz O.A., Mahrous A.M.

Advances in Space Research Vol. 72 ( 3 ) page： 790 - 804 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Advances in Space Research

In this paper, we developed an empirical model for predicting Total Electron Content (TEC) on a single station receiver located within the equatorial anomaly crest region at Helwan – Egypt (29.86°N, 31.32°E & MLAT 27.02°N). The neural network algorithm was developed from several inputs representing diurnal, seasonal, and solar cycle variations, solar and geomagnetic activity, and solar wind parameters using TEC data collected by the SCINDA GPS receiver. The TEC data collected for about nine years from 2009 to 2017 comprises almost the whole solar cycle 24 allowing the developed model to be validated and tested for different solar activity conditions. The 2009 – 2016 dataset was randomly divided into 70% for training, and 30% for validation during model development while the 2017 dataset was reserved for testing the model during independent validation. The validation was done by comparing TEC from the developed model and TEC derived from the GPS scintillation and TEC monitor (GPSTEC). Knowing that TEC modeling over the equatorial anomaly crest regions is challenging since it is characterized by high temporal and spatial variations, the developed model reconstructed diurnal GPSTEC from 2014 to 2016 with a root mean square error (RMSE) of 4.0 TECU and 3.2 TECU for high and low solar activity phases respectively. The neural network (NN) modeled TEC was highly correlated with GPSTEC, that is 0.93 and 0.94 for low and high solar activity respectively. In comparison, the International Reference Ionosphere (IRI)-2016 model predicted the general trend of GPSTEC in 2017 with RMSE of 5.43 TECU better than the developed TEC model with RMSE of 5.74 TECU. However, the NN model predicted diurnal GPSTEC for selected quiet and disturbed days, and seasonal TEC better than the IRI model in 2017. Therefore, the developed model was able to capture temporal ionospheric TEC for diurnal and seasonal variations during low solar activity. It was established that the performance of the empirical model depends on the size and distribution of the data used for model development. It's worth noting that despite the improved performance of the NN algorithm in predicting diurnal and seasonal TEC variation, the NN-modeled TEC performed poorly in reconstructing the nighttime anomalies exhibited in the GPSTEC. The inclusion of the IRI-NmF2 as network input also adds to the improved performance of the network.

DOI： 10.1016/j.asr.2022.10.052

A Ground‐Based Instrument Suite for Integrated High‐Time Resolution Measurements of Pulsating Aurora With Arase Reviewed

K. Hosokawa, S.‐I. Oyama, Y. Ogawa, Y. Miyoshi, S. Kurita, M. Teramoto, S. Nozawa, T. Kawabata, Y. Kawamura, Y.‐M. Tanaka, H. Miyaoka, R. Kataoka, K. Shiokawa, U. Brändström, E. Turunen, T. Raita, M. G. Johnsen, C. Hall, D. Hampton, Y. Ebihara, Y. Kasahara, S. Matsuda, I. Shinohara, R. Fujii

Journal of Geophysical Research: Space Physics Vol. 128 ( 8 ) 2023.8

Statistical Analysis of the Horizontal Phase Velocity Distribution of Atmospheric Gravity Waves and Medium-Scale Traveling Ionospheric Disturbances in Airglow Images Over Darwin (12.4 degrees S, 131.0 degrees E) Reviewed

Tsuboi Takuma, Shiokawa Kazuo, Otsuka Yuichi, Fujinami Hatsuki, Nakamura Takuji, Neudegg David

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 128 ( 8 ) 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

Atmospheric gravity waves (AGWs) and medium-scale traveling ionospheric disturbances (MSTIDs) in the upper atmosphere can be observed in nocturnal airglow images. Spectral analysis of airglow images provides propagation direction and intensity of these waves. However, the spectral analysis of airglow images has not been done yet for stations in the southern hemisphere except for Antarctica. In this study, we calculated the horizontal phase velocity spectra of AGWs in the mesosphere-lower-thermosphere (MLT) region near the mesopause and MSTIDs in the F-region ionosphere from airglow images at wavelengths of 557.7 and 630.0 nm, respectively, by applying the 3-dimensional Fourier spectral analysis to the airglow images obtained at Darwin (12.4°S, 131.0°E) in Australia for 13.75 years from 2001 to 2007 and from 2011 to 2019. The spectra of AGWs in the MLT region show clear characteristics that the southward power spectral density (PSD) is stronger in summer and weaker in winter. Tropospheric convection was located at north of Darwin in summer and above Darwin in winter, suggesting that the tropospheric convection is a possible source of AGWs in the mesopause region. The spectra of MSTIDs in the F-region ionosphere show that the dominant northwestward PSD is stronger in winter and during solar quiet periods. These features can be explained if the observed MSTIDs are caused by the ionospheric instabilities. A weak positive correlation was observed between PSDs of AGWs in the mesosphere and MSTIDs. We propose that the MSTIDs propagating other than northwestward may be generated by AGWs.

DOI： 10.1029/2022JA030769

Spatio-Temporal Characteristics of IPDP-Type EMIC Waves on April 19, 2017: Implications for Loss of Relativistic Electrons in the Outer Belt Reviewed Open Access

Asuka Hirai, Fuminori Tsuchiya, Takahiro Obara, Yuto Katoh, Yoshizumi Miyoshi, Kazuo Shiokawa, Yasumasa Kasaba, Hiroaki Misawa, Chae Woo Jun, Satoshi Kurita, Martin G. Connors, Aaron T. Hendry, Atsuki Shinbori, Yuichi Otsuka, Takuya Tsugawa, Michi Nishioka, Septi Perwitasari, Jerry W. Manweiler

Journal of Geophysical Research: Space Physics Vol. 128 ( 8 ) 2023.8

Language：English Publishing type：Research paper (scientific journal)

To understand the mechanism of the increased frequency of intervals of pulsations of diminishing periods (IPDPs), we analyzed IPDP-type electromagnetic ion cyclotron (EMIC) waves that occurred on 19 April 2017, using ground and satellite observations. Observations by low-altitude satellites and ground-based magnetometers indicate that the increased IPDP frequency is caused by an inward (i.e., Earthward) shift of the EMIC wave source region. The EMIC wave source region moves inward along the mid-latitude trough, which we used as a proxy for the plasmapause location. A statistical analysis shows that increases in the IPDP frequency showed a positive correlation with polar cap potentials. These results suggest an enhanced convection electric field causes an inward shift of the source region. The inward shift of the source region allows EMIC waves to scatter relativistic electrons over a wide range of radial distances during the IPDP event. This mechanism suggests that IPDP-type EMIC waves are more likely to scatter relativistic electrons than other EMIC waves. We also show that the decreased phase-space density of relativistic electrons in the outer radiation belt is consistent with the extent of the source region and the resonant energy of EMIC waves, implying a possible contribution of EMIC waves to outer radiation belt loss during the main phase of geomagnetic storms.

DOI： 10.1029/2023JA031479

Equatorial plasma bubble intensities across longitudinal sectors of the globe using GNSS observations Reviewed

Okoh Daniel, Shiokawa Kazuo, Otsuka Yuichi, Rabiu Babatunde, Habarulema John Bosco, Migoya-Orue Yenca, Cesaroni Claudio

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 249 2023.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Atmospheric and Solar-Terrestrial Physics

We present the first investigation of Equatorial Plasma Bubble (EPB) intensities across longitudinal sectors of the globe using observations from global navigation satellite system (GNSS) receivers. GNSS data from a total of 93 receiver stations located within ±20 degrees of the geomagnetic equator across the globe were used. The data covered periods of years 2014 and 2019 which are respectively years of high and low solar activity in solar cycle 24. We define a parameter known as the Standard deviation of Residual TEC (SRT) to characterize the EPB intensities. The EPB occurrence was defined by day-night differences of the rate of change of TEC index (ROTI). We observed a high correlation (r ∼ 0.80) between the magnitudes of the SRT and ROTI during the EPB occurrence, but the correlation is low (r ∼ 0.37) during non occurrence of EPB. The EPB intensities are greater during seasons with high occurrence rates. The EPB intensities and occurrence rates are also greater during the high solar activity. We found that the post-sunset intensities are greatest in the Atlantic region, followed by the African region, then the American, Australian, Asian, and Pacific regions in that order. The post-midnight intensities are greatest in the African region, followed by the Atlantic, American, Australian, Asian, and Pacific regions in that order.

DOI： 10.1016/j.jastp.2023.106097

IMF Dependence of Midnight Bifurcation in the Thermospheric Wind at an Auroral Latitude Based on Nine Winter Measurements in Tromsø, Norway Reviewed Open Access

S. Oyama, K. Hosokawa, H. Vanhamäki, A. Aikio, T. Sakanoi, L. Cai, I. I. Virtanen, K. Shiokawa, N. Nishitani, A. Shinbori, Y. Ogawa

Geophysical Research Letters Vol. 50 ( 14 ) 2023.7

Interhemispheric Coupling Study by Observations and Modelling (ICSOM): Concept, Campaigns, and Initial Results Reviewed Open Access

Kaoru Sato, Yoshihiro Tomikawa, Masashi Kohma, Ryosuke Yasui, Dai Koshin, Haruka Okui, Shingo Watanabe, Kazuyuki Miyazaki, Masaki Tsutsumi, Damian Murphy, Chris Meek, Yufang Tian, Manfred Ern, Gerd Baumgarten, Jorge L. Chau, Xinzhao Chu, Richard Collins, Patrick J. Espy, Hiroyuki Hashiguchi, Andrew J. Kavanagh, Ralph Latteck, Franz‐Josef Lübken, Marco Milla, Satonori Nozawa, Yasunobu Ogawa, Kazuo Shiokawa, M. Joan Alexander, Takuji Nakamura, William E. Ward

Journal of Geophysical Research: Atmospheres Vol. 128 ( 11 ) 2023.6

Geomagnetic activity dependence and dawn-dusk asymmetry of thermospheric winds from 9-year measurements with a Fabry–Perot interferometer in Tromsø, Norway Reviewed Open Access

Shin-ichiro Oyama, Anita Aikio, Takeshi Sakanoi, Keisuke Hosokawa, Heikki Vanhamäki, Lei Cai, Ilkka Virtanen, Marcus Pedersen, Kazuo Shiokawa, Atsuki Shinbori, Nozomu Nishitani, Yasunobu Ogawa

Earth, Planets and Space Vol. 75 ( 1 ) 2023.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

Ion drag associated with the ionospheric plasma convection plays an important role in the high-latitude thermospheric dynamics, yet changes in the thermospheric wind with geomagnetic activity are not fully understood. We performed a statistical analysis of the thermospheric wind measurements with a Fabry–Perot interferometer (FPI; 630 nm wavelength) in Tromsø, Norway, in the winter months for 9 years. The measurements were sorted by a SuperMAG (SME) index, and a quiet-time wind pattern was defined as an hourly mean under SME ≤ 40 nT. The quiet-time wind pattern can be expected to be represented by a pressure gradient associated with the solar radiation and a geostrophic force balance. With an increase in the geomagnetic activity level, the thermospheric wind turned over from eastward to westward at dusk and increased the equatorward magnitude from midnight to dawn. Deviations from the quiet-time wind presented similar patterns in the direction with the ionospheric plasma convection but were larger in magnitude at dusk than at dawn. This is the first study to report a dawn-dusk asymmetry of the thermospheric wind acceleration feature and signatures of the eastward wind acceleration at dawn by ion drag.

Graphical Abstract

DOI： 10.1186/s40623-023-01829-0

Multi-Event Conjugate Measurements of the SAR Arc Detachment From the Auroral Oval Using DMSP Satellites and an All-Sky Camera at Athabasca, Canada Reviewed

Other Link： https://link.springer.com/article/10.1186/s40623-023-01829-0/fulltext.html

Unsolved problems: Mesoscale polar cap flow channels' structure, propagation, and effects on space weather disturbances Reviewed Open Access

Lyons Larry. R. R., Nishimura Yukitoshi, Liu Jiang, Zou Ying, Bristow William. A. A., Yadav Sneha, Donovan Eric, Nishitani Nozomu, Shiokawa Kazuo, Hosokawa Keisuke

FRONTIERS IN ASTRONOMY AND SPACE SCIENCES Vol. 10 2023.4

Gololobov A., Shiokawa K., Baishev D., Inaba Y., Otsuka Y., Connors M.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 128 ( 4 ) 2023.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

We report the first statistical study of stable auroral red (SAR) arcs detached from the main auroral oval during non-storm time, using multi-event conjugate measurements by the Defense Meteorological Satellite Program (DMSP) satellites (F13–F19) and a ground-based all-sky imager at Athabasca (Canada) (54.6°W, 246.36°Е, MLAT = 61.5°, MLON = 308.3°, L = 4.4). We found 63 events of detached SAR arc conjunctions with the DMSP satellites in the northern hemisphere and 18 events in the opposite southern hemisphere from 2006 to 2018. Measurements aboard DMSP satellites show that detached SAR arcs are in general associated with enhancements of electron temperature (60 cases) and electron density troughs (58 cases). Only 14 cases show strong horizontal flow associated with the detached SAR arcs, indicating that the strong plasma flow is not a necessary condition to cause the detached SAR arcs. The electron temperature measured by DMSP associated with detached SAR arcs positively correlates with F10.7 solar activity index. The measured emission intensities at 630.0 nm in the SAR arcs show a good correlation with the electron temperature. These results indicate that the detached SAR arcs during non-storm time are caused by heat flux from the magnetosphere associated with substorms, and their intensity depends on the background plasma condition in the ionosphere.

DOI： 10.1029/2022JA030544

Multi-Event Analysis of Magnetosphere-Ionosphere Coupling of Nighttime Medium-Scale Traveling Ionospheric Disturbances From the Ground and the Arase Satellite Reviewed Open Access

K. Kawai, K. Shiokawa, Y. Otsuka, S. Oyama, M. G. Connors, Y. Kasahara, Y. Kasaba, S. Nakamura, F. Tsuchiya, A. Kumamoto, A. Shinbori, A. Matsuoka, I. Shinohara, Y. Miyoshi

Journal of Geophysical Research: Space Physics Vol. 128 ( 2 ) 2023.2

Language：English Publishing type：Research paper (scientific journal)

Kawai et al. (2021) reported the first ground-satellite conjugate observation of nighttime medium-scale traveling ionospheric disturbances (MSTIDs), by analyzing measurements from an airglow imager at Gakona (geographic latitude: 62.39°N, geographic longitude: 214.78°E, magnetic latitude: 63.60°N) and the Arase satellite in the magnetosphere on 3 November 2018. The Arase satellite observed variations in both the polarization electric field and the electron density as the Arase footprint passed through the MSTID structures in the ionosphere. In this study, we investigated whether these electric field and density variations associated with MSTIDs at subauroral latitudes are always observed by Arase in the magnetosphere. We used three airglow imagers installed at Gakona, Athabasca (geographic latitude: 54.60°N, geographic longitude: 246.36°E, magnetic latitude: 61.10°N), and Kapuskasing (geographic latitude: 49.39°N, geographic longitude: 277.81°E, magnetic latitude: 58.70°N) and the Arase satellite. We found eight observations of MSTIDs conjugate with Arase. They indicate that electric field and density variations associated with MSTIDs are not always observed in the magnetosphere. These variations tend to be observed in the magnetosphere during geomagnetically quiet times and when the amplitude of the MSTID is large. We categorized the MSTIDs into those caused by plasma instabilities and gravity waves and found that the electric field and density variations can be observed in the magnetosphere for both types of MSTIDs.

DOI： 10.1029/2022JA030542

A Statistical Study of Longitudinal Extent of Pc1 Pulsations Using Seven PWING Ground Stations at Subauroral Latitudes Reviewed Open Access

Jie Liu, Kazuo Shiokawa, Shin‐Ichiro Oyama, Yuichi Otsuka, Chae‐Woo Jun, Masahito Nosé, Tsutomu Nagatsuma, Kaori Sakaguchi, Akira Kadokura, Mitsunori Ozaki, Martin Connors, Dmitry Baishev, Nozomu Nishitani, Alexey Oinats, Vladimir Kurkin, Tero Raita

Journal of Geophysical Research: Space Physics Vol. 128 ( 1 ) 2023.1

Ionospheric Modulation by EMIC Wave-Driven Proton Precipitation: Observations and Simulations Reviewed Open Access

Tian X., Yu Y., Gong F., Ma L., Cao J., Solomon S.C., Shreedevi P.R., Shiokawa K., Otsuka Y., Oyama S.i., Miyoshi Y.

Journal of Geophysical Research Space Physics Vol. 128 ( 1 ) 2023.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

Protons of tens of keV can be resonantly scattered by electromagnetic ion cyclotron (EMIC) waves excited in the magnetosphere, resulting in proton precipitation down to the upper atmosphere. In this study, we report for the first time the ionospheric height-dependent ionization in response to EMIC-associated isolated proton aurora (IPA) using simultaneous space-borne and ground-based measurements. On 06 March 2019, the Polar Orbiting Environmental Satellites observed significant proton precipitation in the dusk sector (MLT ∼ 19), while ground-based magnetometers detected a clear signature of EMIC waves. Meanwhile, the conjugated all sky imager captured an IPA and the nearby Poker Flat incoherent scatter radar (PFISR) showed enhanced electron density in the E region, suggesting a potential consequence of the EMIC wave-driven proton precipitation. The Global Airglow model simulations confirmed the dominant impact of proton precipitation on the ionosphere and agreed well with PFISR observations. This study confirmed physical links from the magnetosphere to the ionosphere through EMIC-driven proton precipitation.

DOI： 10.1029/2022JA030983

ELECTROMAGNETIC ULF/ELF OSCILLATIONS CAUSED BY THE ERUPTION OF THE TONGA VOLCANO Reviewed Open Access

Martines-Bedenko V. A., Pilipenko V. A., Shiokawa K., Akbashev R. R.

SOLAR-TERRESTRIAL PHYSICS Vol. 9 ( 1 ) page： 47 - 55 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Solar-Terrestrial Physics

The eruption of the Tonga volcano on January 13 and 15, 2022 and related intense lightning activity led to the excitation of a number of specific electromagnetic oscillations in different frequency ranges. We examine properties of these oscillations, using data from magnetometers of various types located in Kamchatka and in the Pacific region. We confirmed that there might have been a geomagnetic response to the formation of an acoustic resonance between the Earth surface and the ionosphere: localized harmonic oscillations with a frequency 3.5-4.0 mHz, which lasted for ~1.5 hr, were detected ~15 min after the beginning of the eruption at distance of ~800 km. An increase was observed in the intensity of the Schumann resonance at stations in the Far East. Broadband emission stimulated by intense volcanic lightning was detected to occur in the Pc1 range (2-5 Hz). The emission presumably results from the excitation of the magnetosonic waveguide in the upper ionosphere by lightning activity.

DOI： 10.12737/stp-91202306

Ultra Low Frequency Modulation of Energetic Electron Precipitation in the D-Region Ionosphere in a Magnetically Quiet Time Using OCTAVE Very Low Frequency and Low Frequency (VLF/LF) Observations Reviewed

Kentaro Tanaka, Hiroyo Ohya, Fuminori Tsuchiya, Kenro Nozaki, Mariko Teramoto, Kazuo Shiokawa, Yoshizumi Miyoshi, Martin Connors, Hiroyuki Nakata

URSI Radio Science Letters Vol. 4 2023

SEARCH FOR PULSED ULTRALOW-FREQUENCY ELECTROMAGNETIC EARTHQUAKE PRECURSORS Reviewed Open Access

Martines-Bedenko V.A., Pilipenko V.A., Shiokawa K., Kasimova V.A.

Geophysical Research Vol. 24 ( 2 ) page： 5 - 24 2023

Language：English Publishing type：Research paper (scientific journal) Publisher：Geophysical Research

Numerous publications have appeared in the literature describing a new seismo-electromagnetic effect – the appearance of magnetic pulses with a duration of 1–40 s, which are detected at distances up to ten thousand km several minutes before earthquakes of even low magnitude. An assumption was made about the universality of the processes of impulse precursor generation and the fundamental possibility of a short-term (several minutes) warning of an approaching earthquake. In the presented article, the possibility of the appearance of ultra-low-frequency pulses that precede seismic events with magnitudes M>5.0, according to the data of a network of induction magnetometers in the Far East, is investigated. In the records of these highly sensitive magnetometers, impulse disturbances are constantly encountered, some of which are observed synchronously at several stations, which eliminates the influence of local noise. The spectral maximum of about 7–8 Hz of the oscillatory structure, which manifests itself in many pulses, corresponds to the fundamental frequency of the Schumann resonator. A comparison of magnetic observations with data from the WWLLN (World Wide Lightning Location Network) showed that some of the pulses were caused by lightning discharges in the 650 km vicinity of magnetic station. Despite the fact that some of the impulses are observed immediately before earthquakes, it is impossible to speak with confidence about their connection with seismic activity. The calculation of the number of impulses in the 5-min interval before and after the seismic shock shows that they are randomly distributed relative to the moment of the earthquake. Apparently, the pulses are predominantly due to the ionospheric response to a far lightning discharge.

DOI： 10.21455/gr2023.2-1

Relationship between geomagnetic storms and occurrence of ionospheric irregularities in the west sector of Africa during the peak of the 24th solar cycle Reviewed Open Access

Ondede George Ochieng, Rabiu A. B., Okoh Daniel, Baki Paul, Olwendo Joseph, Shiokawa Kazuo, Otsuka Yuichi

FRONTIERS IN ASTRONOMY AND SPACE SCIENCES Vol. 9 2022.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Frontiers in Astronomy and Space Sciences

The study of ionospheric irregularities is important since many technological systems might be influenced by the ionosphere. In this work, we use data from the Global Navigation Satellite Systems (GNSS) receiver installed in Abuja, Nigeria, GPS Scintillation Network Decision Aid (SCINDA) TEC data from the Air Force Research Laboratory (AFRL) data archive, and the geomagnetic data from the World Data Center (WDC) in Kyoto, Japan, to investigate the relationship between geomagnetic storm and ionospheric irregularity occurrences using the rate of change of total electron content (TEC) index (ROTI), with a validation using the S4 indices, during the peak of the 24th solar cycle. The occurrences of irregularities were investigated on day-to-day and seasonal bases. The nighttime ionospheric irregularities, which are attributed to ionospheric plasma irregularities in the equatorial ionospheric F-region, were found to be prevalent. To investigate the relationship between the strength of ionospheric irregularities (ROTI) and the geomagnetic storm (Dst), the periodogram power spectral density (PSD) and regression analysis were used. The results showed that there was no correlation, cc = 0.073, between the Dst and ROTI, implying that the strengths of ionospheric irregularities occurring during geomagnetic storms are not strictly decided by the magnitudes of the storms; this was also confirmed using the S4 index. The impact of geomagnetic storms caused enhanced development or inhibition of ionospheric irregularities. We observed that the bulk of the storms occurring during the period of this study is not associated with ionospheric irregularities. Finally, the investigation showed that the correlation between the ROTI and Dst observed during the coronal mass ejection (CME)-driven geomagnetic storms was higher than that during the corotating interaction region (CIR)-driven geomagnetic storms, during the peak of the 24th solar cycle. The results of this work confirm the findings by other researchers.

DOI： 10.3389/fspas.2022.969235

Observation of source plasma and field variations of a substorm brightening aurora at L ∼ 6 by a ground‐based camera and the Arase satellite on 12 October 2017 Reviewed

L. Chen, K. Shiokawa, Y. Miyoshi, S. Oyama, C‐W. Jun, Y. Ogawa, K. Hosokawa, Y. Inaba, Y. Kazama, S. Y. Wang, S. W. Y. Tam, T. F. Chang, B. J. Wang, K. Asamura, S. Kasahara, S. Yokota, T. Hori, K. Keika, Y. Kasaba, A. Kumamoto, F. Tsuchiya, M. Shoji, Y. Kasahara, A. Matsuoka, I. Shinohara, S. Imajo, S. Nakamura, M. Kitahara

Journal of Geophysical Research: Space Physics Vol. 127 ( 11 ) 2022.11

Thermospheric wind response to a sudden ionospheric variation in the trough: Event at a pseudo breakup during geomagnetically quiet conditions Reviewed Open Access

S.-i. Oyama, H. Vanhamäki, L. Cai, A. Aikio, M. Rietveld, Y. Ogawa, T. Raita, M. Kellinsalmi, K. Kauristie, B. Kozelov, A. Shinbori, K. Shiokawa, T. T. Tsuda, T. Sakanoi

Earth Planets Space Vol. 74 ( 1 ) page： 154 2022.10

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

The thermospheric wind response to a sudden westward turning of the ion velocity at a high latitude was studied by analyzing data obtained with a Fabry-Perot interferometer (FPI; 630 nm), Dynasonde, and Swarm A & C satellites during a conjunction event. The event occurred during a geomagnetically quiet period (Kp= 0+) through the night, but some auroral activity occurred in the north. The collocated FPI and Dynasonde measured the thermospheric wind (U) and ionospheric plasma velocity (V), respectively, in the F region at the equatorward trough edge. A notable scientific message from this study is the possible role of thermospheric wind in the energy dissipation process at F-region altitude. The FPI thermospheric wind did not instantly follow a sudden V change due to thermospheric inertia in the F region. At a pseudo-breakup during the event, V suddenly changed direction from eastward to westward within 10 min. U was concurrently accelerated westward, but its development was more gradual than that of V, with U remaining eastward for a while after the pseudo-breakup. The delay of U is attributed to the thermospheric inertia. During this transition interval, U.V was negative, which would result in more efficient generation of frictional heating than the positive U.V case. The sign of U.V, which is related to the relative directions of the neutral wind and plasma drift, is important because of its direct impact on ion-neutral energy exchange during collisions. This becomes especially important during substorm events, where rapid plasma velocity changes are common. The sign of U.V may be used as an indicator to find the times and locations where thermospheric inertia plays a role in the energy dissipation process.

DOI： 10.1186/s40623-022-01710-6

Three-Dimensional Fourier Analysis of Atmospheric Gravity Waves and Medium-Scale Traveling Ionospheric Disturbances Observed in Airglow Images in Hawaii Over Three Years Reviewed

Localized mesospheric ozone destruction corresponding to isolated proton aurora coming from Earth's radiation belt. Reviewed International journal Open Access

Mitsunori Ozaki, Kazuo Shiokawa, Ryuho Kataoka, Martin Mlynczak, Larry Paxton, Martin Connors, Satoshi Yagitani, Shion Hashimoto, Yuichi Otsuka, Satoshi Nakahira, Ian Mann

Scientific reports Vol. 12 ( 1 ) page： 16300 - 16300 2022.10

Language：English Publishing type：Research paper (scientific journal)

Relativistic electron precipitation (REP) from the Earth's radiation belt plays an important role in mesospheric ozone loss as a connection between space weather and the climate system. However, the rapid (tens of minutes) destruction of mesospheric ozone directly caused by REP has remained poorly understood due to the difficulty of recognizing its location and duration. Here we show a compelling rapid correspondence between localized REP and ozone destruction during a specific auroral phenomenon, the called an isolated proton aurora (IPA). The IPA from the Earth's radiation belt becomes an important spatial and temporal proxy of REP, distinct from other auroral phenomena, and allowing visualizing micro-ozone holes. We found ozone destruction of as much as 10-60% within 1.5 h of the initiation of IPA. Electromagnetic ion cyclotron waves in the oxygen ion band observed as the driver of REP likely affect through resonance with mainly ultra-relativistic (> 2 mega-electron-volts) energy electrons. The rapid REP impact demonstrates its crucial role and direct effect on regulating the atmospheric chemical balance.

DOI： 10.1038/s41598-022-20548-2

Hideto Naito, Kazuo Shiokawa, Yuichi Otsuka, Hatsuki Fujinami, Takuma Tsuboi, Takeshi Sakanoi, Akinori Saito, Takuji Nakamura

Journal of Geophysical Research: Space Physics Vol. 127 ( 10 ) 2022.10

Language：English Publishing type：Research paper (scientific journal)

Three-dimensional Fourier spectral analysis of airglow images is a useful technique to provide propagation characteristics of atmospheric gravity waves (AGWs) in the mesopause region and medium-scale traveling ionospheric disturbances (MSTIDs) in the thermosphere observed at emission wavelengths of 557.7 nm (altitudes: 90–100 km for AGWs) and 630.0 nm (200–300 km for MSTIDs). However, a statistical study of spectral analysis of airglow images over years has not been done yet at Hawaii. Here, we report the first spectral analysis of AGWs and MSTIDs using airglow images obtained at Haleakala (20.71°N, 203.74°E), Hawaii, during the three years from 2013 to 2016. The power spectral density (PSD) of AGWs tends to be larger toward north to northeast in summer and from north to west and southward in winter. The eastward (summer) and westward (winter) preferences are consistent with a wind-filtering mechanism of AGWs by a mesospheric jet. Some correspondence is found between the locations of tropospheric convection activities and AGW propagation directions, suggesting that these mesospheric AGWs are originated from the troposphere. The PSDs of MSTIDs are larger in solstice than in equinox. This PSD enhancement in solstice is consistent with a sporadic-E (Es) layer occurrence in either northern or southern hemisphere, suggesting that the MSTIDs over Hawaii could be caused by a coupling process between the Perkins and Es layer instabilities. A small correlation was found between the PSDs of AGWs in the mesopause region and the PSDs of MSTIDs, suggesting that the MSTIDs are partly caused by AGWs from the mesopause region.

DOI： 10.1029/2022JA030346

Multi-Event Study of Simultaneous Observations of Isolated Proton Auroras at Subauroral Latitudes Using Ground All-Sky Imagers and the Van Allen Probes Reviewed

Nakamura Kohki, Shiokawa Kazuo, Nose Masahito, Nagatsuma Tsutomu, Sakaguchi Kaori, Spence Harlan, Reeves Geoff, Funsten Herbert O., MacDowall Robert, Smith Charles, Wygant John, Bonnell John, Mann Ian R.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 127 ( 9 ) 2022.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

Isolated proton auroras (IPAs) appearing at subauroral latitudes are generated by energetic protons precipitating from the magnetosphere through interaction with electromagnetic ion cyclotron (EMIC) waves. Thus, an IPA is the ionospheric projection of the spatial and temporal variation of wave-particle interaction regions in the magnetosphere. In this study, we conducted unique multi-event analysis of simultaneous observations of IPAs and their source regions on 22 April, 7 September, and 22 March 2018, using all-sky imagers at subauroral latitudes and the Van Allen Probes. When the satellite footprint passed over the IPAs associated with ground Pc1 geomagnetic pulsations, locally generated He+-band EMIC waves with the same frequencies as the ground Pc1 pulsations were observed in all events. The IPAs and EMIC waves had comparable narrow widths in the latitudinal direction. The EMIC waves appeared during the rapid enhancement of the ring current proton flux at energy range of ∼10–50 keV, while they disappeared at the rapid decrease of the electron density. From these results, we conclude that the boundaries of the localized IPAs and EMIC waves were determined by the overlap region of energetic proton enhancement and the plasmasphere. This overlap of ring-current protons and plasmasphere is a favorable condition for the pitch-angle scattering of protons by the EMIC waves. Characteristic magnetic and electric field variations with the IPAs were not observed by the satellite, indicating that the IPAs were not accompanied by field-aligned currents comparable to that of oval auroral arcs.

DOI： 10.1029/2022JA030455

Statistical Study of Subauroral Arc Detachment at Athabasca, Canada: New Insights on STEVE Reviewed

Yadav Sneha, Shiokawa Kazuo, Otsuka Yuichi, Connors Martin

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 127 ( 9 ) 2022.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

We present the first comparative statistical study of subauroral arc detachment from the main auroral oval at Athabasca (magnetic latitude = 61.5°N), Canada, for three different types of subauroral arcs: pure red arc, red arc with simultaneous emission in green-line (red + green arc), and STEVE (strong thermal emission velocity enhancement). Based on 15-years (2006–2020) of all-sky imaging observations, this study not only uncovers the occurrence characteristics of different arcs but also provides important insights into the specific geomagnetic conditions under which STEVE develops. Red arc was the most common subauroral arc (139 events), followed by red + green arc (42 events), and STEVE (26 events) was a rare phenomenon. The detachment rate of red and red + green arcs exhibits dependence on both the solar flux and geomagnetic activity. The detachment rate of STEVE was higher during premidnight, whereas that of red and red + green arcs was higher around the midnight sector. The geomagnetic activity was relatively higher for STEVE, the decrease in the AL index and local X-component magnetic variations being ∼2–3 times higher for STEVE as compared to other arcs. STEVE shows a strong association with asymmetric ring current in terms of prominent bay-like enhancement in ASY-H index prior to its detachment. Such bay-like enhancement was ∼4 times higher for STEVE as compared to other arcs. STEVE events were accompanied by dispersionless injection for both electron and proton flux at geosynchronous orbit. These results unambiguously suggest that STEVE develops after substorm associated energy injection and significant intensification of the asymmetric ring current.

DOI： 10.1029/2021JA029856

Quantifying the Size and Duration of a Microburst‐Producing Chorus Region on 5 December 2017 Reviewed Open Access

S. S. Elliott, A. W. Breneman, C. Colpitts, J. M. Pettit, C. A. Cattell, A. J. Halford, M. Shumko, J. Sample, A. T. Johnson, Y. Miyoshi, Y. Kasahara, C. M. Cully, S. Nakamura, T. Mitani, T. Hori, I. Shinohara, K. Shiokawa, S. Matsuda, M. Connors, M. Ozaki, J. Manninen

Geophysical Research Letters Vol. 49 ( 15 ) page： e2022GL099655 2022.8

A Story of Developing the Idea of Plasma-Sheet Flow Braking Reviewed Open Access

Shiokawa Kazuo

FRONTIERS IN ASTRONOMY AND SPACE SCIENCES Vol. 9 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Frontiers in Astronomy and Space Sciences

This paper reports a story of developing the idea of Earthward ion flow braking in the near-Earth plasma sheet and its relationship with substorm onset processes. This idea and the data that support it are the basis for today’s two competing models for substorms: the near-Earth neutral-line model and the current disruption model. The idea was developed when the author was staying at the Max Planck Institute for Extraterrestrial Physics (MPE) from July 1996 to June 1997. The story addresses the colleagues and mentors who had contributed to the development of this idea. The lessons learned from this story are also summarized for students and early-career scientists for their development of new scientific ideas.

DOI： 10.3389/fspas.2022.957776

Collaborative Research Activities of the Arase and Van Allen Probes Reviewed Open Access

Y. Miyoshi, I. Shinohara, S. Ukhorskiy, S. G. Claudepierre, T. Mitani, T. Takashima, T. Hori, O. Santolik, I. Kolmasova, S. Matsuda, Y. Kasahara, M. Teramoto, Y. Katoh, M. Hikishima, H. Kojima, S. Kurita, S. Imajo, N. Higashio, S. Kasahara, S. Yokota, K. Asamura, Y. Kazama, S.-Y. Wang, C.-W. Jun, Y. Kasaba, A. Kumamoto, F. Tsuchiya, M. Shoji, S. Nakamura, M. Kitahara, A. Matsuoka, K. Shiokawa, K. Seki, M. Nosé, K. Takahashi, C. Martinez-Calderon, G. Hospodarsky, C. Colpitts, Craig Kletzing, J. Wygant, H. Spence, D. N. Baker, G. D. Reeves, J. B. Blake, L. Lanzerotti

Space Science Reviews Vol. 218 ( 5 ) page： 38 2022.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

This paper presents the highlights of joint observations of the inner magnetosphere by the Arase spacecraft, the Van Allen Probes spacecraft, and ground-based experiments integrated into spacecraft programs. The concurrent operation of the two missions in 2017–2019 facilitated the separation of the spatial and temporal structures of dynamic phenomena occurring in the inner magnetosphere. Because the orbital inclination angle of Arase is larger than that of Van Allen Probes, Arase collected observations at higher $L$-shells up to $L \sim 10$. After March 2017, similar variations in plasma and waves were detected by Van Allen Probes and Arase. We describe plasma wave observations at longitudinally separated locations in space and geomagnetically-conjugate locations in space and on the ground. The results of instrument intercalibrations between the two missions are also presented. Arase continued its normal operation after the scientific operation of Van Allen Probes completed in October 2019. The combined Van Allen Probes (2012-2019) and Arase (2017-present) observations will cover a full solar cycle. This will be the first comprehensive long-term observation of the inner magnetosphere and radiation belts.

DOI： 10.1007/s11214-022-00885-4

Other Link： https://link.springer.com/article/10.1007/s11214-022-00885-4/fulltext.html

Signatures of Auroral Potential Structure Extending Through the Near‐Equatorial Inner Magnetosphere Reviewed Open Access

S. Imajo, Y. Miyoshi, K. Asamura, I. Shinohara, M. Nosé, K. Shiokawa, Y. Kasahara, Y. Kasaba, A. Matsuoka, S. Kasahara, S. Yokota, K. Keika, T. Hori, M. Shoji, S. Nakamura, M. Teramoto

Geophysical Research Letters Vol. 49 ( 10 ) 2022.5

Slow Contraction of Flash Aurora Induced by an Isolated Chorus Element Ranging From Lower-Band to Upper-Band Frequencies in the Source Region Reviewed Open Access

Mitsunori Ozaki, Satoshi Yagitani, Kazuo Shiokawa, Yoshimasa Tanaka, Yasunobu Ogawa, Keisuke Hosokawa, Yoshiya Kasahara, Yusuke Ebihara, Yoshizumi Miyoshi, Kousuke Imamura, Ryuho Kataoka, Shin-ichiro Oyama, Teppei Chida, Akira Kadokura

GEOPHYSICAL RESEARCH LETTERS Vol. 49 ( 9 ) 2022.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Flash aurora driven by an isolated chorus element can be a useful ionospheric indicator for identifying the source wave properties via wave-particle interactions. Using ground observation and modeling approaches, here we report the temporal characteristics of flash aurora that depend on the chorus frequency width and the sweep rate. We found that the contraction time increases more than the expansion time in patchy auroral variations, due to the difference in the minimum electron energies resonated with the chorus wave packet away from the equatorial source to higher latitudes. Especially, the contraction time strongly depends on the higher-frequency chorus waves due to cyclotron resonance with lower-energy electrons. The model calculations support that the chorus element ranges from lower-band to upper-band frequencies with respect to half the gyrofrequency at the exact generation region. Our study provides the prompt (milliseconds) chorus-driven electron dynamics through the spatiotemporal characteristics of flash aurora in the ionosphere.

DOI： 10.1029/2021GL097597

Detecting Equatorial Plasma Bubbles on All-Sky Imager Images Using Convolutional Neural Network Reviewed

Statistical survey of Arase satellite data sets in conjunction with the Finnish Riometer Network Reviewed Open Access

Neethal Thomas, Antti Kero, Yoshizumi Miyoshi, Kazuo Shiokawa, Miikka Hyötylä, Tero Raita, Yoshiya Kasahara, Iku Shinohara, Shoya Matsuda, Satoko Nakamura, Satoshi Kasahara, Shoichiro Yokota, Kunihiro Keika, Tomoaki Hori, Takefumi Mitani, Takeshi Takashima, Kazushi Asamura, Yoichi Kazama, Shiang‐Yu Wang, C‐W. Jun, Nana Higashio

Journal of Geophysical Research: Space Physics Vol. 127 ( 5 ) 2022.5

Simultaneous Observations of EMIC‐Induced Drifting Electron Holes (EDEHs) in the Earth's Radiation Belt by the Arase Satellite, Van Allen Probes, and THEMIS Reviewed Open Access

S. Nakamura, Y. Miyoshi, K. Shiokawa, Y. Omura, T. Mitani, T. Takashima, N. Higashio, I. Shinohara, T. Hori, S. Imajo, A. Matsuoka, F. Tsuchiya, A. Kumamoto, Y. Kasahara, M. Shoji, H. Spence, V. Angelopoulos

Geophysical Research Letters Vol. 49 ( 5 ) 2022.3

Srisamoodkham W., Shiokawa K., Otsuka Y., Ansari K., Jamjareegulgarn P.

Lecture Notes in Networks and Systems Vol. 461 page： 481 - 487 2022

Language：English Publishing type：Research paper (scientific journal) Publisher：Lecture Notes in Networks and Systems

This paper proposes initially to apply convolutional neural network (CNN) for detecting the equatorial plasma bubbles on the ASI images. The considered CNN model is the YOLO v3 tiny model under a deep learning API (Keras), running on top of the machine learning platform (TensorFlow). Our program for EPB detection is written in Python that is extended easily to combine into a space weather web site for detecting and notifying EPBs in our next step. The results show that the YOLO v3-based CNN can detect the EPBs in ASI images with different intensities obtained from many countries. The threshold is tested and selected to be 0.40 suitably for detecting the anomaly (EPB existence). The maximum anomalous value is selected to decide the EPB occurrence.

DOI： 10.1007/978-981-19-2130-8_38

Spatio-Temporal Distributions of Lightning Stroke Charge Using ELF and Meteorological Data Reviewed

Variations of Zonal Wind Velocity in the Thermosphere Observed at Southeast Asian Sector During Quiet and Active Geomagnetic Days Reviewed

Sarudin Idahwati, Hamid Nurul Shayana Abdul, Abdullah Mardina, Rusli Fatin Nur Syakirah Mohd, Otsuka Yuichi, Shiokawa Kazuo, Yatini Clara, Komonjinda Siramas, Somboon Ekkarach

JURNAL FIZIK MALAYSIA Vol. 43 ( 1 ) page： 10025 - 10035 2022

Yasuhide Hobara, Takuhiko Ohashi, Tomonori Shiraishi, Kazuo Shiokawa

Lecture Notes in Electrical Engineering Vol. 842 page： 329 - 337 2022

Language：English Publishing type：Research paper (international conference proceedings)

In this paper lightning stroke charges are estimated remotely by using combinations of Extremely Low Frequency (ELF) radio waves, conventional Lightning Locating System (LLS) and local meteorological information for the first time. Each lightning stroke location from LLS and corresponding transient signature of ELF magnetic field observed at a long distance (−1000 km between lightning stroke and observation site) are utilized to estimate the charge moment change (CMC) of the lightning stroke. The lightning stroke charge Q is then derived by dividing the CMC by the altitude of the neutralized lightning charge. The corresponding altitude of the neutralized lightning charge for each stroke is determined by assuming local −20 °C altitude for a positive stroke (−10 °C altitude for a negative strokes) from MesoScale Model (MSM). Spatial and temporal frequency distributions of energetic lightning (large amount of stroke charge) and cumulative frequency distributions of stroke charge in northwestern part of Japan in local summer and winter seasons for 4 years were derived. The spatial occurrence frequency distributions indicate that lightning strokes with a large amount of neutralized charge occur more frequently in inland areas during summertime and in coastal areas in winter. The cumulative frequency distribution indicates that positive polarity lightning strokes in winter tend to have a large charge. Our statistical results are in good agreement with the lightning properties inferred from local observations, and are considered to be useful information not only to study electrical properties of thunderstorms but also for future maintenance planning of power grid systems in wide areas and mitigation of lightning damages.

DOI： 10.1007/978-981-16-8690-0_30

RESPONSE OF THE D-REGION IONOSPHERE TO FIREBALLS USING VLF/LF TRANSMITTER SIGNALS Reviewed Open Access

Takeru Suzuki, Hiroyo Ohya, Fuminori Tsuchiya, Kazuo Shiokawa, Hiroyuki Nakata

18th Annual Meeting of the Asia Oceania Geosciences Society page： 215 - 217 2022

Horizontal Inhomogeneity in the D-Region Ionosphere During an X-Class Solar Flare Determined by OCTAVE VLF Observations Reviewed

Masaharu Nakayama, Hiroyo Ohya, Fuminori Tsuchiya, Kenro Nozaki, Kazuo Shiokawa, Hiroyuki Nakata

URSI Radio Science Letters Vol. 4 2022

Spatio-Temporal Characteristics of Energetic Lightning in Southeast Asia: Preliminary Statistical Results Reviewed

Shunsuke Akama, Yasuhide Hobara, Amir Izzani Mohamed, Chandima Gomes, Kazuo Shiokawa, Shu Hirai, Hiroshi Kikuchi, Michael Stock

Lecture Notes in Electrical Engineering Vol. 842 page： 317 - 327 2022

Language：English Publishing type：Research paper (international conference proceedings)

The region of Southeast Asia is known as one of the lightning-prone areas in the world. However, spatial and temporal distributions of high-energy lightning discharges, which cause natural disasters e.g. significant damages to local power grid systems and forest fires, are still unknown. This paper reports initial results on the statistical characteristics of energetic lightning around Malay Peninsula. Highly accurate timing and location as well as lightning peak current (Ip ) of lightning strokes were obtained by ENTLN (Earth Networks Total Lightning Network), while the vertical charge moment change Qds as a proxy of high-energy lightning was derived by using ground-based ELF magnetic field observations in Pahang, Malaysia with a small threshold of less than 10 C·km. The characteristics of energetic lightning for both rainy and dry seasons were successfully derived for the first time in this region. The results indicate that highly energetic lightning occur frequently throughout the rainy and dry seasons, mainly over the Malacca Strait. Long-term statistical analysis with an extended data analysis period is necessary to understand further the seasonal and yearly dependences of energetic lightning and their relations with local climate conditions.

DOI： 10.1007/978-981-16-8690-0_29

Predictability of variable solar-terrestrial coupling Reviewed Open Access

Daglis Ioannis A., Chang Loren C., Dasso Sergio, Gopalswamy Nat, Khabarova Olga V, Kilpua Emilia, Lopez Ramon, Marsh Daniel, Matthes Katja, Nandy Dibyendu, Seppala Annika, Shiokawa Kazuo, Thieblemont Remi, Zong Qiugang

ANNALES GEOPHYSICAE Vol. 39 ( 6 ) page： 1013 - 1035 2021.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Annales Geophysicae

In October 2017, the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP) Bureau established a committee for the design of SCOSTEP's Next Scientific Programme (NSP). The NSP committee members and authors of this paper decided from the very beginning of their deliberations that the predictability of the Sun-Earth System from a few hours to centuries is a timely scientific topic, combining the interests of different topical communities in a relevant way. Accordingly, the NSP was christened PRESTO -PREdictability of the variable Solar-Terrestrial cOupling. This paper presents a detailed account of PRESTO; we show the key milestones of the PRESTO roadmap for the next 5 years, review the current state of the art and discuss future studies required for the most effective development of solar-terrestrial physics.

DOI： 10.5194/angeo-39-1013-2021

Auroral Heating of Plasma Patches Due to High-Latitude Reconnection Reviewed

Pena Joaquin Diaz, Semeter Joshua, Nishimura Yukitoshi, Varney Roger, Reimer Ashton, Hairston Marc, Zettergren Matthew, Hirsch Michael, Verkhoglyadova Olga, Hosokawa Keisuke, Shiokawa Kazuo

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 126 ( 12 ) 2021.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

This study exploits the volumetric sampling capabilities of the Resolute Bay Incoherent Scatter Radar (RISR-N) in collaboration with all-sky imagery and in situ measurements to examine the interplay between cold plasma transport and auroral precipitation during a high-latitude lobe reconnection event on the dawn side. Solar wind IMF preceding the event was characterized by an impulsive negative excursion in Bz embedded within a period of Bz > 0 and By < 0. The combined effects of transport and magnetic stress release associated with a high-latitude reconnection pulse drove a co-mingling between patches and soft electron precipitation, creating common regions of elevated electron density and temperature. Vertical ionospheric profiles extracted in the rest frame of the drifting patch showed a contemporaneous increase in Te above 200 km and Ne below 250 km while at the same time showing only a small impact in Ne near the F-region peak. The observations suggest a new mechanism for creating a “hot patch” wherein the density enhancement is not generated by the precipitation but is warmed by it. The physics-based GEMINI model was used to explore the response to the observed precipitation as a function of altitude and time. Model results suggest that a correlated enhancement in Ne and Te at DMSP altitudes (∼800 km), that is, hot patch, can be produced by auroral heating and upward diffusion, irrespective of lower altitude density structure. The study highlights the need for densely distributed observations in space and time for understanding both mesoscale and small-scale ionospheric dynamics in regions subject to complex forcing.

DOI： 10.1029/2021JA029657

Periodicities and Colors of Pulsating Auroras: DSLR Camera Observations From the International Space Station Reviewed

Study of an Equatorward Detachment of Auroral Arc From the Oval Using Ground‐Space Observations and the BATS‐R‐US–CIMI Model Reviewed Open Access

Sneha Yadav, K. Shiokawa, S. Oyama, Y. Inaba, N. Takahashi, K. Seki, K. Keika, Tzu‐Fang Chang, S. W. Y. Tam, B.‐J. Wang, Y. Kazama, S.‐Y. Wang, K. Asamura, S. Kasahara, S. Yokota, T. Hori, Y. Kasaba, F. Tsuchiya, A. Kumamoto, M. Shoji, Y. Kasahara, A. Matsuoka, S. Matsuda, C.‐W. Jun, S. Imajo, Y. Miyoshi, I. Shinohara

Journal of Geophysical Research: Space Physics Vol. 126 ( 12 ) 2021.12

Multipoint Measurement of Fine‐Structured EMIC Waves by Arase, Van Allen Probe A, and Ground Stations Reviewed Open Access

S. Matsuda, Y. Miyoshi, Y. Kasahara, L. Blum, C. Colpitts, K. Asamura, Y. Kasaba, A. Matsuoka, F. Tsuchiya, A. Kumamoto, M. Teramoto, S. Nakamura, M. Kitahara, I. Shinohara, G. Reeves, H. Spence, K. Shiokawa, T. Nagatsuma, S. Oyama, I. R. Mann

Geophysical Research Letters Vol. 48 ( 23 ) 2021.11

Nanjo Sota, Hozumi Yuta, Hosokawa Keisuke, Kataoka Ryuho, Miyoshi Yoshizumi, Oyama Shin-ichiro, Ozaki Mitsunori, Shiokawa Kazuo, Kurita Satoshi

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 126 ( 10 ) 2021.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

We investigated the spatial characteristics of pulsating auroras (PsA) using digital camera measurements from the International Space Station. These measurements covered PsAs in (Formula presented.) 5-h wide regions in the magnetic local time (MLT) direction in short time intervals ((Formula presented.) 10 min). Analyses of two events suggested that the periodicity of the main pulsation of a PsA does not exhibit any clear dependence on the magnetic latitude (63– (Formula presented.)) and MLT (00–05). These results suggest that the periods are not controlled by the bounce time of trapped electrons but by local conditions such as gradients of temperature and/or density of electrons near the magnetospheric source region. We also analyzed the colors of PsAs as proxies for the energies of precipitating electrons. The blue and green channels of the digital camera are sensitive to the band emission of molecular nitrogen ions and the green line of oxygen atoms, respectively. Because the energy bands of precipitating electrons producing those two emissions are different, ratios of blue to green (B/G ratios) can be used as proxies for the energies of PsA electrons. The B/G ratio tends to be higher in the morning sector than in the midnight sector, which is consistent with the results of previous studies showing the MLT dependence of the energies of PsA electrons. This capability of estimating the energies of auroral electrons from digital camera images is expected to provide more opportunities for citizen scientists to contribute more deeply to auroral science.

DOI： 10.1029/2021JA029564

Isolated Proton Aurora Driven by EMIC Pc1 Wave: PWING, Swarm, and NOAA POES Multi-Instrument Observations Reviewed Open Access

Hyangpyo Kim, Kazuo Shiokawa, Jaeheung Park, Yoshizumi Miyoshi, Yukinaga Miyashita, Claudia Stolle, Hyunju Kim Connor, Junga Hwang, Stephan Buchert, Hyuck Jin Kwon, Satoko Nakamura, Kohki Nakamura, Shin Ichiro Oyama, Yuichi Otsuka, Tsutomu Nagatsuma, Kaori Sakaguchi

Geophysical Research Letters Vol. 48 ( 18 ) 2021.9

Language：English Publishing type：Research paper (scientific journal)

We report the concurrent observations of F-region plasma changes and field-aligned currents (FACs) above isolated proton auroras (IPAs) associated with electromagnetic ion cyclotron Pc1 waves. Key events on March 19, 2020 and September 12, 2018 show that ground magnetometers and all-sky imagers detected concurrent Pc1 wave and IPA, during which NOAA POES observed precipitating energetic protons. In the ionospheric F-layer above the IPA zone, the Swarm satellites observed transverse Pc1 waves, which span wider latitudes than IPA. Around IPA, Swarm also detected the bipolar FAC and localized plasma density enhancement, which is occasionally surrounded by wide/shallow depletion. This indicates that wave-induced proton precipitation contributes to the energy transfer from the magnetosphere to the ionosphere.

DOI： 10.1029/2021GL095090

An experimental investigation into the possible connections between the zonal neutral wind speeds and equatorial plasma bubble drift velocities over the African equatorial region Reviewed Open Access

Okoh D. I, Rabiu A. B., Shiokawa K., Otsuka Y., Wu Q., Seemala G. K., Katamzi-Joseph Z. T.

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 220 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Atmospheric and Solar-Terrestrial Physics

There is increasing interest to understand thermospheric neutral wind and ionized plasma coupling, especially by using empirical observations. This is the first study that reports simultaneous measurements of thermospheric neutral wind and equatorial plasma bubble (EPB) speeds over the African equatorial region. Neutral wind speeds were obtained using a Fabry-Perot interferometer (FPI), while EPB speeds were obtained using an all-sky optical imager. Both instruments are co-located in Abuja (Geographic: 8.99°N, 7.38°E; Geomagnetic: 1.60°S). Data for 11 nights of coincident neutral wind and EPB speed observations were used. The neutral wind speeds were in the range of about −30 to 300 m/s, while EPB speeds were in the range of about 15–400 m/s. The speeds of both neutral winds and EPBs were generally observed to be faster during the early night hours and to slow down towards midnight. In some instances, the neutral wind and EPB speeds were comparable, an observation that is in agreement with full development of the F region dynamo. There were also instances in which the EPBs were faster or slower than the neutral winds. In one of the nights, a southward turning of the IMF-Bz was observed to cause a sudden increase in the EPB speed. For some nights, the neutral winds were faster than the EPBs during earlier hours of the nights, and the disparity reduced during the later hours of the nights. This was attributed to the possibility that the F region dynamo was yet to be fully developed during the earlier hours.

DOI： 10.1016/j.jastp.2021.105663

First Simultaneous Observation of a Night Time Medium‐Scale Traveling Ionospheric Disturbance From the Ground and a Magnetospheric Satellite Reviewed Open Access

K. Kawai, K. Shiokawa, Y. Otsuka, S. Oyama, Y. Kasaba, Y. Kasahara, F. Tsuchiya, A. Kumamoto, S. Nakamura, A. Matsuoka, S. Imajo, Y. Kazama, S.‐Y. Wang, S. W. Y. Tam, T. F. Chang, B. J. Wang, K. Asamura, S. Kasahara, S. Yokota, K. Keika, T. Hori, Y. Miyoshi, C. Jun, M. Shoji, I. Shinohara

Journal of Geophysical Research: Space Physics Vol. 126 ( 9 ) 2021.9

Multi-instrument study of longitudinal wave structures for plasma bubble seeding in the equatorial ionosphere Reviewed Open Access

Takahashi H., Essien P., Figueiredo C. A. O. B., Wrasse C. M., Barros D., Abdu M. A., Otsuka Y., Shiokawa K., Li GuoZhu

EARTH AND PLANETARY PHYSICS Vol. 5 ( 5 ) page： 368 - 377 2021.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Earth and Planetary Physics

Large Scale Wave Structures (LSWS) in the equatorial ionospheric F-region were observed by measuring spatial and temporal variations within detrended total electron content (dTEC) data obtained by ground-based GNSS receivers over the South American continent. By using dTEC-maps, we have been able to produce, for the first-time, two-dimensional representations of LSWS. During the period from September to December, the LSWS frequently occurred starting a few hours prior to Equatorial Plasma Bubble (EPB) development. From 17 events of LSWS observed in 2014 and 2015, wave characteristics were obtained: the observed wavelengths, periods, and the phase speeds are respectively, ~900 km, ~41 min and ~399 m/s; the waves propagated from the northeast to southeast. In some cases the front of the oscillation was meridionally aligned, extending to more than 1600 km, the first time such large extension of the wavefront has been reported. From F-layer bottom height oscillation data, measured by ionosonde, LSWS exhibit two different vertical phase propagation modes, in-phase and downward phase. The former mode indicates the presence of a polarization electric field in the F-layer bottom side; the latter suggests propagation of atmospheric gravity waves. The presence of LSWS near the solar terminator, followed by the development of EPBs, suggests that the upwelling of the F-layer bottom height produces a condition favorable to the development of Rayleigh–Taylor instability.

DOI： 10.26464/epp2021047

PSTEP: project for solar-terrestrial environment prediction Reviewed International journal Open Access

Kanya Kusano, Kiyoshi Ichimoto, Mamoru Ishii, Yoshizumi Miyoshi, Shigeo Yoden, Hideharu Akiyoshi, Ayumi Asai, Yusuke Ebihara, Hitoshi Fujiwara, Tada-Nori Goto, Yoichiro Hanaoka, Hisashi Hayakawa, Keisuke Hosokawa, Hideyuki Hotta, Kornyanat Hozumi, Shinsuke Imada, Kazumasa Iwai, Toshihiko Iyemori, Hidekatsu Jin, Ryuho Kataoka, Yuto Katoh, Takashi Kikuchi, Yuki Kubo, Satoshi Kurita, Haruhisa Matsumoto, Takefumi Mitani, Hiroko Miyahara, Yasunobu Miyoshi, Tsutomu Nagatsuma, Aoi Nakamizo, Satoko Nakamura, Hiroyuki Nakata, Naoto Nishizuka, Yuichi Otsuka, Shinji Saito, Susumu Saito, Takashi Sakurai, Tatsuhiko Sato, Toshifumi Shimizu, Hiroyuki Shinagawa, Kazuo Shiokawa, Daikou Shiota, Takeshi Takashima, Chihiro Tao, Shin Toriumi, Satoru Ueno, Kyoko Watanabe, Shinichi Watari, Seiji Yashiro, Kohei Yoshida, Akimasa Yoshikawa

EARTH PLANETS AND SPACE Vol. 73 ( 1 ) 2021.8

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

Although solar activity may significantly impact the global environment and socioeconomic systems, the mechanisms for solar eruptions and the subsequent processes have not yet been fully understood. Thus, modern society supported by advanced information systems is at risk from severe space weather disturbances. Project for solar-terrestrial environment prediction (PSTEP) was launched to improve this situation through synergy between basic science research and operational forecast. The PSTEP is a nationwide research collaboration in Japan and was conducted from April 2015 to March 2020, supported by a Grant-in-Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan. By this project, we sought to answer the fundamental questions concerning the solar-terrestrial environment and aimed to build a next-generation space weather forecast system to prepare for severe space weather disasters. The PSTEP consists of four research groups and proposal-based research units. It has made a significant progress in space weather research and operational forecasts, publishing over 500 refereed journal papers and organizing four international symposiums, various workshops and seminars, and summer school for graduate students at Rikubetsu in 2017. This paper is a summary report of the PSTEP and describes the major research achievements it produced.

DOI： 10.1186/s40623-021-01486-1

Does Solar Variation Change Earth's Environment?

SHIOKAWA Kazuo

TRENDS IN THE SCIENCES Vol. 26 ( 8 ) page： 8_18 - 8_21 2021.8

Spatial Evolution of Wave‐Particle Interaction Region Deduced From Flash‐Type Auroras and Chorus‐Ray Tracing Reviewed Open Access

Mitsunori Ozaki, Tomohiro Inoue, Yoshimasa Tanaka, Satoshi Yagitani, Yoshiya Kasahara, Kazuo Shiokawa, Yoshizumi Miyoshi, Kousuke Imamura, Keisuke Hosokawa, Shin‐ichiro Oyama, Ryuho Kataoka, Yusuke Ebihara, Yasunobu Ogawa, Akira Kadokura

Journal of Geophysical Research: Space Physics Vol. 126 ( 7 ) 2021.7

What controls the luminosity of polar cap airglow patches?: Implication from airglow measurements in Eureka, Canada in comparison with SuperDARN convection pattern Reviewed Open Access

Hosokawa K., Nagata M., Shiokawa K., Otsuka Y.

POLAR SCIENCE Vol. 28 2021.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Polar Science

Polar cap patches are known as islands of enhanced electron density in the polar cap F region ionosphere. To observe the airglow signature of polar cap patches continuously at a fixed point near the center of the MLAT/MLT coordinate system, we started operating an all-sky imager in Eureka, Canada since 2015, where the magnetic latitude is ~87°. By statistically analyzing the 630-nm airglow images from Eureka, it was identified that the luminosity of patches, which is proportional to the electron density in the F region, increases during specific UT interval from 16 to 22 UT. This outstanding UT variation of patch luminosity can be explained simply by the systematic shift of the terminator in the MLAT/MLT coordinate system due to the offset between the geographic and geomagnetic pole. That is, the spatial relationship between the dense source plasma in the sunlit area and the high-latitude convection system controls the UT variation. We also found that when the IMF By is positive, the number of polar cap patches was twice of that in the negative IMF By. By deriving average convection patterns from the archived SuperDARN map potential data, we confirmed that the configuration of plasma convection is more appropriate for patches to be transported toward the magnetic pole during the positive IMF By condition.

DOI： 10.1016/j.polar.2020.100608

Influence of Zonal Wind Velocity Variation on Equatorial Plasma Bubble Occurrences Over Southeast Asia Reviewed

Sarudin I., Hamid N. S. A., Abdullah M., Buhari S. M., Shiokawa K., Otsuka Y., Hozumi K., Jamjareegulgarn P.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 126 ( 5 ) 2021.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

The present study aims to investigate the influence of the zonal wind velocity on equatorial plasma bubble (EPB) occurrences over Southeast Asia. The observation of the EPB occurrence is obtained from the GPS Rate of TEC change index. Meanwhile, the zonal winds were measured using a Fabry-Perot interferometer located at Kototabang and Chiang Mai stations, and the height of F layer was acquired using an ionosonde at Chumphon station near the magnetic equator. This is the first study to report the influence of zonal wind velocity variation on EPB occurrences with the presence and absence of EPB using GPS data in the Southeast Asian sector. The results illustrated that the average magnitude of zonal wind velocity during the presence of EPB (78 ± 23 m/s) was higher than that of its absence (68 ± 21 m/s). It was observed using long-term data analyses which led to in-depth analyses. The analysis of temporal variation of zonal wind variation demonstrated that the zonal winds during EPB were higher in the evening compared to midnight and postmidnight periods from medium to high solar activities. The dependence of zonal wind velocity on EPB over local time was obtained based on the analysis which utilized the data collected during equinox in high solar activity. Besides that, a positive correlation was obtained between the zonal wind velocity and EPB occurrences during pre-reversal enhancement (PRE) corroborated the effects of zonal wind influence on PRE, and thus EPB occurrences.

DOI： 10.1029/2020JA028994

Simultaneous Observation of Two Isolated Proton Auroras at Subauroral Latitudes by a Highly Sensitive All-Sky Camera and Van Allen Probes Reviewed Open Access

Nakamura Kohki, Shiokawa Kazuo, Otsuka Yuichi, Shinbori Atsuki, Miyoshi Yoshizumi, Connors Martin, Spence Harlan, Reeves Geoff, Funsten Herbert O., MacDowall Robert, Smith Charles, Wygant John, Bonnell John

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 126 ( 5 ) 2021.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

Isolated proton auroras (IPAs) appearing at subauroral latitudes are generated by energetic protons precipitating from the magnetosphere through interaction with electromagnetic ion cyclotron (EMIC) waves. An IPA thus indicates the spatial scale and temporal variation of wave-particle interactions in the magnetosphere. In this study, a unique event of simultaneous ground and magnetospheric satellite observations of two IPAs were conducted on March 16, 2015, using an all-sky imager at Athabasca, Canada and Van Allen Probes. The Van Allen Probes observed two isolated EMIC waves with frequencies of ∼1 and 0.4 Hz at L ≈ 5.0 when the satellite footprint crossed over the two IPAs. This suggests that the IPAs were caused by localized EMIC waves. Proton flux at 5–20 keV increased locally when the EMIC waves appeared. Electron flux at energies below ∼500 eV also increased. Temperature anisotropy of the energetic protons was estimated at 1.5–2.5 over a wide L-value range of 3.0–5.2. Electron density gradually decreased from L = 3.5 to 5.4, suggesting that the EMIC wave at L ≈ 5.0 was located in the gradual plasmapause. From these observations, we conclude that the localized IPAs and associated EMIC waves took place because of localized enhancement of energetic proton flux and plasma density structure near the plasmapause. The magnetic field observed by the satellite showed small variation during the wave observation, indicating that the IPAs were accompanied by the weak field-aligned current.

DOI： 10.1029/2020JA029078

Preface of the special issue: "Variability of the Sun and Its Terrestrial Impact (VarSITI) Completion Symposium 2019 and the SCOSTEP 14th Quadrennial Solar-Terrestrial Physics Symposium (STP14)" Preface Reviewed

Multi‐Event Analysis of Plasma and Field Variations in Source of Stable Auroral Red (SAR) Arcs in Inner Magnetosphere During Non‐Storm‐Time Substorms Reviewed Open Access

Yudai Inaba, Kazuo Shiokawa, Shin‐ichiro Oyama, Yuichi Otsuka, Martin Connors, Ian Schofield, Yoshizumi Miyoshi, Shun Imajo, Atsuki Shinbori, Artem Yu Gololobov, Yoichi Kazama, Shiang‐Yu Wang, Sunny W. Y. Tam, Tzu‐Fang Chang, Bo‐Jhou Wang, Kazushi Asamura, Shoichiro Yokota, Satoshi Kasahara, Kunihiro Keika, Tomoaki Hori, Ayako Matsuoka, Yoshiya Kasahara, Atsushi Kumamoto, Shoya Matsuda, Yasumasa Kasaba, Fuminori Tsuchiya, Masafumi Shoji, Masahiro Kitahara, Satoko Nakamura, Iku Shinohara, Harlan E. Spence, Geoff D. Reeves, Robert J. Macdowall, Charles W. Smith, John R. Wygant, John W. Bonnell

Journal of Geophysical Research: Space Physics Vol. 126 ( 4 ) 2021.4

Shiokawa Kazuo, Dasso Sergio, Miteva Rositsa, Pallamraju Duggirala, Zhang Shun-Rong

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 215 2021.4

Development of research capacities in space weather: a successful international cooperation Reviewed Open Access

Amory-Mazaudier Christine, Radicella Sandro, Doherty Patricia, Gadimova Sharafat, Fleury Rolland, Nava Bruno, Anas Emran, Petitdidier Monique, Migoya-Orue Yenca, Alazo-Cuartas Katy, Shiokawa Kazuo

JOURNAL OF SPACE WEATHER AND SPACE CLIMATE Vol. 11 2021.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Space Weather and Space Climate

This paper presents an international cooperation which has successfully developed research capacities in the scientific disciplines of sun-earth relations and space weather in many countries over the world during the past decades. This success was based on the deployment of scientific instruments in countries that did not have them, on the sharing of knowledge and research tools, on thesis supervision and on the integration of researchers trained in their country. This article will only focus on aspects of training conducted by ICTP, Boston College, ICG, SCOSTEP and GIRGEA. We will highlight what has been enhanced in international cooperation to achieve this success and what remains to be done.

DOI： 10.1051/swsc/2021006

Magnetic Conjugacy of Pc1 Waves and Isolated Proton Precipitation at Subauroral Latitudes: Importance of Ionosphere as Intensity Modulation Region Reviewed Open Access

Mitsunori Ozaki, Kazuo Shiokawa, Richard B. Horne, Mark J. Engebretson, Marc Lessard, Yasunobu Ogawa, Keisuke Hosokawa, Masahito Nosé, Yusuke Ebihara, Akira Kadokura, Satoshi Yagitani, Yoshizumi Miyoshi, Shion Hashimoto, Shipra Sinha, Ashwini K. Sinha, Gopi K. Seemala, Chae‐Woo Jun

Geophysical Research Letters Vol. 48 ( 5 ) 2021.3

A review of the SCOSTEP's 5-year scientific program VarSITI-Variability of the Sun and Its Terrestrial Impact Reviewed Open Access

Shiokawa Kazuo, Georgieva Katya

PROGRESS IN EARTH AND PLANETARY SCIENCE Vol. 8 ( 1 ) 2021.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Earth and Planetary Science

The Sun is a variable active-dynamo star, emitting radiation in all wavelengths and solar-wind plasma to the interplanetary space. The Earth is immersed in this radiation and solar wind, showing various responses in geospace and atmosphere. This Sun–Earth connection variates in time scales from milli-seconds to millennia and beyond. The solar activity, which has a ~11-year periodicity, is gradually declining in recent three solar cycles, suggesting a possibility of a grand minimum in near future. VarSITI—variability of the Sun and its terrestrial impact—was the 5-year program of the scientific committee on solar-terrestrial physics (SCOSTEP) in 2014–2018, focusing on this variability of the Sun and its consequences on the Earth. This paper reviews some background of SCOSTEP and its past programs, achievements of the 5-year VarSITI program, and remaining outstanding questions after VarSITI. [Figure not available: see fulltext.]

DOI： 10.1186/s40645-021-00410-1

GPS Scintillations and TEC Variations in Association With a Polar Cap Arc Reviewed Open Access

Wang Yong, Cao Zheng, Xing Zan-Yang, Zhang Qing-He, Jayachandran P. T., Oksavik K., Balan Nanan, Shiokawa K.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 126 ( 3 ) 2021.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

A unique example of a polar cap arc producing clear amplitude and phase scintillations in GPS L-band signals is presented using observations from an all-sky imager and a GPS receiver and a digital ionosonde at Resolute Bay and the SuperDARN Inuvik radar. During the southward interplanetary magnetic field (IMF) condition, the polar cap arc moved quickly from the dusk-side to the midnight auroral oval at a speed of ∼700 m/s, as revealed by all-sky 557.7 and 630.0 nm images. When it intersected the raypath of GPS signals, both amplitude and phase scintillations appeared, which is very different from previous results. Moreover, the scintillations were precisely determined through power spectral analysis. We propose that the strong total electron content (TEC) enhancement (∼6 TECU) and flow shears in association with the polar cap arc under the southward IMF condition were creating the scintillations. It provides evidence for the existence of polar cap arc scintillations that may be harmful for satellite applications even through L-band signals.

DOI： 10.1029/2020JA028968

Investigation of Small‐Scale Electron Density Irregularities Observed by the Arase and Van Allen Probes Satellites Inside and Outside the Plasmasphere Reviewed Open Access

Neethal Thomas, Kazuo Shiokawa, Yoshizumi Miyoshi, Yoshiya Kasahara, Iku Shinohara, Atsushi Kumamoto, Fuminori Tsuchiya, Ayako Matsuoka, Satoshi Kasahara, Shoichiro Yokota, Kunihiro Keika, Tomoaki Hori, Kazushi Asamura, Shiang‐Yu Wang, Yoichi Kazama, Sunny Wing‐Yee Tam, Tzu‐Fang Chang, Bo‐Jhou Wang, John Wygant, Aaron Breneman, Geoffrey Reeves

Journal of Geophysical Research: Space Physics Vol. 126 ( 3 ) 2021.3

Statistical Analysis of Pc1 Wave Ducting Deduced From Swarm Satellites Reviewed Open Access

Kim Hyangpyo, Shiokawa Kazuo, Park Jaeheung, Miyoshi Yoshizumi, Stolle Claudia, Buchert Stephan

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 126 ( 3 ) 2021.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

Transverse Pc1 waves propagating from magnetospheric source regions undergo mode conversion to the compressional mode in the ionosphere due to the induced Hall current. Mode converted Pc1 waves propagate across the magnetic field through the ionospheric waveguide. This process is called Pc1 wave ducting (PWD). PWDs have been observed by magnetometers on both ground and low Earth orbit satellites over a wide latitudinal and longitudinal range. In this work, we present the statistical analysis results of PWD exploiting Swarm satellites from 2015 to 2019. Spatial distributions show that the PWDs are mainly observed over the South Atlantic Anomaly longitudes, possibly due to the high Hall conductivity and F-region density, and at subauroral/auroral latitudes ((Formula presented.) MLAT). The occurrence rate of PWD increases with increasing AE and (Formula presented.) SYM-H (Formula presented.) indices. Seasonal dependence shows that PWD exhibits a high occurrence rate during equinox and local summer while local winter hosts only a low occurrence. The asymmetry between summer and winter can be explained by the ionospheric plasma density. The high occurrence rate in equinox may result from intense geomagnetic activity during the equinox, probably due to the Russell-McPherron effect. From our statistical analysis, we conclude that the occurrence of PWD is controlled by both ionospheric plasma conditions and geomagnetic activity, and that the mode conversion and PWD occur more efficiently as plasma density increases.

DOI： 10.1029/2020JA029016

Formation of an additional density peak in the bottom side of the sodium layer associated with the passage of multiple mesospheric frontal systems Reviewed Open Access

Viswanathan Lakshmi Narayanan, Satonori Nozawa, Shin-Ichiro Oyama, Ingrid Mann, Kazuo Shiokawa, Yuichi Otsuka, Norihito Saito, Satoshi Wada, Takuya D. Kawahara, Toru Takahashi

ATMOSPHERIC CHEMISTRY AND PHYSICS Vol. 21 ( 4 ) page： 2343 - 2361 2021.2

Language：English Publishing type：Research paper (scientific journal) Publisher：COPERNICUS GESELLSCHAFT MBH

We present a detailed investigation of the formation of an additional sodium density peak at altitudes of 79-85 km below the main peak of the sodium layer based on sodium lidar and airglow imager measurements made at Ramfjordmoen near Tromso, Norway, on the night of 19 December 2014. The airglow imager observations of OH emissions revealed four passing frontal systems that resembled mesospheric bores, which typically occur in ducting regions of the upper mesosphere. For about 1.5 h, the lower-altitude sodium peak had densities similar to that of the main peak of the layer around 90 km. The lower-altitude sodium peak weakened and disappeared soon after the fourth front had passed. The fourth front had weakened in intensity by the time it approached the region of lidar beams and disappeared soon afterwards. The column-integrated sodium densities increased gradually during the formation of the lower-altitude sodium peak. Temperatures measured with the lidar indicate that there was a strong thermal duct structure between 87 and 93 km. Furthermore, the temperature was enhanced below 85 km. Horizontal wind magnitudes estimated from the lidar showed strong wind shears above 93 km. We conclude that the combination of an enhanced stability region due to the temperature profile and intense wind shears have provided ideal conditions for evolution of multiple mesospheric bores revealed as frontal systems in the OH images. The downward motion associated with the fronts appeared to have brought air rich in H and O from higher altitudes into the region below 85 km, wherein the temperature was also higher. Both factors would have liberated sodium atoms from the reservoir species and suppressed the reconversion of atomic sodium into reservoir species so that the lower-altitude sodium peak could form and the column abundance could increase. The presented observations also reveal the importance of mesospheric frontal systems in bringing about significant variation of minor species over shorter temporal intervals.

DOI： 10.5194/acp-21-2343-2021

Multi-Wavelength Imaging Observations of STEVE at Athabasca, Canada Reviewed Open Access

Yadav Sneha, Shiokawa Kazuo, Otsuka Yuichi, Connors Martin, St Maurice J-P

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 126 ( 2 ) 2021.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

We present the first multi-wavelength imaging observations of strong thermal emission velocity enhancement (STEVE) using an all-sky imager at Athabasca (magnetic latitude = 61.5°N), Canada. This study is based on three STEVE events which were accompanied by picket fence structures in the green-line. Although the STEVE arc was dominant in 630 and 557.7-nm, weak emissions were also found in other wavelengths including OI at 844.6, Hβ, Na, and the nominal background filter at 572.5-nm. As observed at 630 and 557.7-nm, the STEVE arc started as a faint arc close to the auroral oval and moved equatorward. The 557.7-nm arc exhibited picket fence structure at later times after it moved equatorward. The picket fence was sometimes found to persist even after the 630-nm arc had disappeared. During a particular event, the STEVE arcs in both the 630 and 557.7-nm were found to carry a ribbon-like motion moving along the arc. We have found that STEVE arcs are embedded in a region of weak diffuse auroral emissions. The STEVE arcs have sharp boundaries and these boundaries are different in red- and green-line. The sharp decrease in the intensity at the immediate poleward edge of the STEVE arc appears as a “dark-band” in the green-line images. Based on the horizontal component of the geomagnetic field at Fort Smith (magnetic latitude 67.28°N), we find that the STEVE arc detachment, its equatorward motion, and its brightness coincided with changes in the magnetic activity during the recovery phase of a substorm.

DOI： 10.1029/2020JA028622

Study of Spatiotemporal Development of Global Distribution of Magnetospheric ELF/VLF Waves Using Ground‐Based and Satellite Observations, and RAM‐SCB Simulations, for the March and November 2017 Storms Reviewed Open Access

Multievent Study of Characteristics and Propagation of Naturally Occurring ELF/VLF Waves Using High‐Latitude Ground Observations and Conjunctions With the Arase Satellite Reviewed Open Access

C. Martinez‐Calderon, Y. Katoh, J. Manninen, O. Santolik, Y. Kasahara, S. Matsuda, A. Kumamoto, F. Tsuchiya, A. Matsuoka, M. Shoji, M. Teramoto, I. Shinohara, K. Shiokawa, Y. Miyoshi

Journal of Geophysical Research: Space Physics Vol. 126 ( 2 ) 2021.2

Yuhei Takeshita, Kazuo Shiokawa, Yoshizumi Miyoshi, Mitsunori Ozaki, Yoshiya Kasahara, Shin‐ichiro Oyama, Martin Connors, Jyrki Manninen, Vania K. Jordanova, Dmitry Baishev, Alexey Oinats, Vladimir Kurkin

Journal of Geophysical Research: Space Physics Vol. 126 ( 2 ) 2021.2

Active auroral arc powered by accelerated electrons from very high altitudes Reviewed Open Access

Shun Imajo, Yoshizumi Miyoshi, Yoichi Kazama, Kazushi Asamura, Iku Shinohara, Kazuo Shiokawa, Yoshiya Kasahara, Yasumasa Kasaba, Ayako Matsuoka, Shiang-Yu Wang, Sunny W. Y. Tam, Tzu-Fang Chang, Bo-Jhou Wang, Vassilis Angelopoulos, Chae-Woo Jun, Masafumi Shoji, Satoko Nakamura, Masahiro Kitahara, Mariko Teramoto, Satoshi Kurita, Tomoaki Hori

SCIENTIFIC REPORTS Vol. 11 ( 1 ) page： 1610 2021.1

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE RESEARCH

Bright, discrete, thin auroral arcs are a typical form of auroras in nightside polar regions. Their light is produced by magnetospheric electrons, accelerated downward to obtain energies of several kilo electron volts by a quasi-static electric field. These electrons collide with and excite thermosphere atoms to higher energy states at altitude of similar to 100 km; relaxation from these states produces the auroral light. The electric potential accelerating the aurora-producing electrons has been reported to lie immediately above the ionosphere, at a few altitudes of thousand kilometres(1). However, the highest altitude at which the precipitating electron is accelerated by the parallel potential drop is still unclear. Here, we show that active auroral arcs are powered by electrons accelerated at altitudes reaching greater than 30,000 km. We employ high-angular resolution electron observations achieved by the Arase satellite in the magnetosphere and optical observations of the aurora from a ground-based all-sky imager. Our observations of electron properties and dynamics resemble those of electron potential acceleration reported from low-altitude satellites except that the acceleration region is much higher than previously assumed. This shows that the dominant auroral acceleration region can extend far above a few thousand kilometres, well within the magnetospheric plasma proper, suggesting formation of the acceleration region by some unknown magnetospheric mechanisms.

DOI： 10.1038/s41598-020-79665-5

An Ephemeral Red Arc Appeared at 68° MLat at a Pseudo Breakup During Geomagnetically Quiet Conditions Reviewed Open Access

S. Oyama, A. Shinbori, Y. Ogawa, M. Kellinsalmi, T. Raita, A. Aikio, H. Vanhamäki, K. Shiokawa, I. Virtanen, L. Cai, A. B. Workayehu, M. Pedersen, K. Kauristie, T. T. Tsuda, B. Kozelov, A. Demekhov, A. Yahnin, F. Tsuchiya, A. Kumamoto, Y. Kasahara, A. Matsuoka, M. Shoji, M. Teramoto, M. Lester

Journal of Geophysical Research: Space Physics Vol. 125 ( 10 ) 2020.10

Plasma and Field Observations in the Magnetospheric Source Region of a Stable Auroral Red (SAR) Arc by the Arase Satellite on 28 March 2017 Reviewed Open Access

Yudai Inaba, Kazuo Shiokawa, Shin-ichiro Oyama, Yuichi Otsuka, Arto Oksanen, Atsuki Shinbori, Artem Yu Gololobov, Yoshizumi Miyoshi, Yoichi Kazama, Shiang-Yu Wang, Sunny W. Y. Tam, Tzu-Fang Chang, Bo-Jhou Wang, Shoichiro Yokota, Satoshi Kasahara, Kunihiro Keika, Tomoaki Hori, Ayako Matsuoka, Yoshiya Kasahara, Atsushi Kumamoto, Yasumasa Kasaba, Fuminori Tsuchiya, Masafumi Shoji, Iku Shinohara, Claudia Stolle

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 125 ( 10 ) 2020.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

A stable auroral red (SAR) arc is an aurora with a dominant 630 nm emission at subauroral latitudes. SAR arcs have been considered to occur due to the spatial overlap between the plasmasphere and the ring-current ions. In the overlap region, plasmaspheric electrons are heated by ring-current ions or plasma waves, and their energy is then transferred down to the ionosphere where it causes oxygen red emission. However, there have been no study conducted so far that quantitatively examined plasma and electromagnetic fields in the magnetosphere associated with SAR arc. In this paper, we report the first quantitative evaluation of conjugate measurements of a SAR arc observed at 2204 UT on 28 March 2017 and investigate its source region using an all-sky imager at Nyrola (magnetic latitude: 59.4 degrees N), Finland, and the Arase satellite. The Arase observation shows that the SAR arc appeared in the overlap region between a plasmaspheric plume and the ring-current ions and that electromagnetic ion cyclotron waves and kinetic Alfven waves were not observed above the SAR arc. The SAR arc was located at the ionospheric trough minimum identified from a total electron content map obtained by the GNSS receiver network. The Swarm satellite flying in the ionosphere also passed the SAR arc at similar to 2320 UT and observed a decrease in electron density and an increase in electron temperature during the SAR-arc crossing. These observations suggest that the heating of plasmaspheric electrons via Coulomb collision with ring-current ions is the most plausible mechanism for the SAR-arc generation.Plain Language Summary A stable auroral red (SAR) arc is an aurora with an optical red emission at latitudes slightly lower than the auroral zone. SAR arcs have been considered to occur due to the spatial overlap between the low-energy plasmaspheric electrons and the high-energy ring-current ions. In the overlap region, plasmaspheric electrons are heated by ring-current ions or plasma waves, and their energy is then transferred down to the upper atmosphere to cause the red emission. However, there have been no study conducted so far that quantitatively examined plasma and electromagnetic fields in the magnetospheric source region of SAR arcs. In this paper, we report the first quantitative evaluation of a SAR arc using an all-sky imager at Nyrola, Finland, and the Arase satellite. The Arase observation shows that the SAR arc appeared in the overlap region between a plasmaspheric plume and the ring-current ions in the inner magnetosphere. The electromagnetic waves associated with the SAR arc were not observed. These observations suggest that the heating of plasmaspheric electrons by ring-current ions is the most plausible mechanism for the SAR-arc generation. This result provides direct evidence of the previous theoretical expectation on the generation mechanism of red aurora at lower latitudes.

DOI： 10.1029/2020JA028068

Statistical study of EMIC Pc1-Pc2 waves observed at subauroral latitudes Reviewed

Jong-Woo Kwon, Khan-Hyuk Kim, Ho Jin, Hyuck-Jin Kwon, Geonhwa Jee, Kazuo Shiokawa, Martin Connors

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 205 2020.9

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Although the occurrence rate of electromagnetic ion cyclotron (EMIC) waves is high in the outer magnetosphere (L > 7), it has been suggested in the past that a steep plasma density gradient region of the plasmapause is a preferred location for the generation of EMIC waves. To examine spectral properties of the EMIC waves occurred near the nominal location of the plasmapause (L = 4-5), we focus on Pc1-Pc2 waves observed at subauroral latitude Athabasca station (magnetic latitude: similar to 62 degrees, and L similar to 4.6). A statistical study of 10,494 wave samples identified from Athabasca data for 2007-2008 reveals the following wave characteristics. (1) Wave frequencies are higher in the postmidnight-to-dawn sector and lower in the late afternoon sector. (2) They mostly appear to be in frequency band between helium and oxygen gyrofrequencies (i.e., He-band) calculated from the dipole field model magnetic field intensity at L = 4.6. (3) The occurrence rate of Pc1-Pc2 waves has a peak in the prenoon sector at 0900-1100 LT under quiet geomagnetic conditions (Kp. 1), but is peaked in the afternoon sector under moderate and disturbed geomagnetic conditions (Kp. 2). (4) The Pc1-Pc2 waves observed at Athabasca were composed of a mixture of left-hand, right-hand, and linearly polarized waves. By comparing previous and recent studies with these observations, we suggest that the subauroral latitude Pc1-Pc2 waves are associated with EMIC waves generated near the plasmapause and discuss the EMIC wave properties in a region of cold and dense plasmas containing heavy ions in the inner magnetosphere.

DOI： 10.1016/j.jastp.2020.105292

Equatorial Plasma Bubble Occurrence Under Propagation of MSTID and MLT Gravity Waves Reviewed Open Access

Takahashi H., Wrasse C. M., Figueiredo C. A. O. B., Barros D., Paulino I., Essien P., Abdu M. A., Otsuka Y., Shiokawa K.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 125 ( 9 ) 2020.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

We observed a signature of equatorial plasma bubbles (EPBs) followed by a medium-scale traveling ionospheric disturbance (MSTID) crossing the solar terminator over the geomagnetic equator during the period of post-sunset rise (PSSR) of the F layer. Simultaneous observations of the EPBs and the MSTIDs by ground-based Global Navigation Satellite System receivers and OI 630-nm imagers, ionospheric parameters by ionosondes, and mesosphere–lower thermosphere (MLT) gravity waves (MLT-GWs) by OH airglow imagers have been carried out in the equatorial and low-latitude region of Brazil. On 16–17 September 2015, MSTIDs with very fast horizontal phase speeds, propagating toward northeast (NE), were observed over the latitude region of 0–30°S in the afternoon to evening time zone. It was geomagnetically quiet time (Kp: 2–3). An EPB development was observed after one of the MSTIDs crossed the solar terminator at 22:00 UT. Large-scale MLT-GWs with slower phase speeds were also observed both at São João do Cariri (7.5°S, 35.0°W) propagating from southwest (SW) to NE and Cachoeira Paulista (22.7°S, 45.0°W) propagating northward. This is to report on what we consider as a signature of direct seeding of EPBs by an MSTID that was likely induced by a secondary GW from tropospheric deep cloud convections to the south. This study highlights a possible dynamical process from the troposphere to ionosphere via this vertical coupling process over the 2,500 km of horizontal distance.

DOI： 10.1029/2019JA027566

The Solar Wind Density Control on the Prompt Penetration Electric Field and Equatorial Electrojet Reviewed

Spatial Extent of Quasiperiodic Emissions Simultaneously Observed by Arase and Van Allen Probes on 29 November 2018 Reviewed Open Access

C. Martinez‐Calderon, F. Němec, Y. Katoh, K. Shiokawa, C. Kletzing, G. Hospodarsky, O. Santolik, Y. Kasahara, S. Matsuda, A. Kumamoto, F. Tsuchiya, A. Matsuoka, M. Shoji, M. Teramoto, S. Kurita, Y. Miyoshi, M. Ozaki, N. Nishitani, A. V. Oinats, V. I. Kurkin

Journal of Geophysical Research: Space Physics Vol. 125 ( 9 ) 2020.9

Nilam B., Ram S. Tulasi, Shiokawa K., Balan N., Zhang Q.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 125 ( 9 ) 2020.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

Prompt penetration of convection/overshielding electric fields to equatorial and low latitudes during the southward/northward turnings of interplanetary magnetic field (IMF Bz) have been widely studied in the literature. The other types of penetration electric fields due to sudden changes in the solar wind dynamic pressure, IMF By and during the onset of substorms have also been recently reported. In this paper, we present the exclusive role of solar wind density changes on the prompt equatorial electric field disturbances using the long-term observations of equatorial electrojet (EEJ) from the Indian sector. In response to the sharp increases in the solar wind density, prompt increases/decreases in the EEJ indicating the eastward/westward prompt penetration electric field (PPEF) of ~20 min periods have been consistently observed on the dayside/nightside. The prompt equatorial electric field disturbances of the opposite polarity have also been observed when the density decreases sharply. Further, the polarity of these PPEF disturbances does not show any clear dependency on the direction of IMF Bz and By. This paper is the first report with a statistically significant number of observations on the characteristics of equatorial electric field disturbances in response to the sudden enhancements/decreases in the solar wind density alone on both dayside and nightside. The underlying physical mechanisms for the prompt equatorial electric field disturbances have been discussed in light of enhanced high-latitude convection and additional field-aligned currents due to sudden enhancement of solar wind density.

DOI： 10.1029/2020JA027869

Ionospheric Plasma Density Oscillation Related to EMIC Pc1 Waves Reviewed Open Access

Hyangpyo Kim, Kazuo Shiokawa, Jaeheung Park, Yoshizumi Miyoshi, Yukinaga Miyashita, Claudia Stolle, Khan-Hyuk Kim, Juergen Matzka, Stephan Buchert, Tanja Fromm, Junga Hwang

GEOPHYSICAL RESEARCH LETTERS Vol. 47 ( 15 ) 2020.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report the first observation of plasma density oscillations coherent with magnetic Pc1 waves. Swarm satellites observed compressional Pc1 wave activity in the 0.5-3 Hz band, which was coherent with in situ plasma density oscillations. Around the Pc1 event location, the Antarctic Neumayer Station III (L similar to 4.2) recorded similar Pc1 events in the horizontal component while NOAA-15 observed isolated proton precipitations at energies above 30 keV. All these observations support that the compressional Pc1 waves at Swarm are oscillations converted from electromagnetic ion cyclotron (EMIC) waves coming from the magnetosphere. The magnetic field and plasma density oscillate in-phase. We compared the amplitudes of density and magnetic field oscillations normalized to background values and found that the density power is much larger than the magnetic field power. This difference cannot be explained by a simple magnetohydrodynamic (MHD) model, although steep horizontal/vertical gradients of background ionospheric density can partly reconcile the discrepancy.

DOI： 10.1029/2020GL089000

Arase observation of the source region of auroral arcs and diffuse auroras in the inner magnetosphere Reviewed

Oxygen torus and its coincidence with EMIC wave in the deep inner magnetosphere: Van Allen Probe B and Arase observations Reviewed Open Access

M. Nosé, A. Matsuoka, A. Kumamoto, Y. Kasahara, M. Teramoto, S. Kurita, J. Goldstein, L. M. Kistler, S. Singh, A. Gololobov, K. Shiokawa, S. Imajo, S. Oimatsu, K. Yamamoto, Y. Obana, M. Shoji, F. Tsuchiya, I. Shinohara, Y. Miyoshi, W. S. Kurth, C. A. Kletzing, C. W. Smith, R. J. MacDowall, H. Spence, G. D. Reeves

Earth, Planets and Space Vol. 72 ( 1 ) page： 111 2020.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

<title>Abstract</title>
We investigate the longitudinal structure of the oxygen torus in the inner magnetosphere for a specific event found on 12 September 2017, using simultaneous observations from the Van Allen Probe B and Arase satellites. It is found that Probe B observed a clear enhancement in the average plasma mass (<italic>M</italic>) up to 3–4 amu at <italic>L</italic> = 3.3–3.6 and magnetic local time (MLT) = 9.0 h. In the afternoon sector at MLT ~ 16.0 h, both Probe B and Arase found no clear enhancements in <italic>M</italic>. This result suggests that the oxygen torus does not extend over all MLT but is skewed toward the dawn. Since a similar result has been reported for another event of the oxygen torus in a previous study, a crescent-shaped torus or a pinched torus centered around dawn may be a general feature of the O+ density enhancement in the inner magnetosphere. We newly find that an electromagnetic ion cyclotron (EMIC) wave in the H+ band appeared coincidently with the oxygen torus. From the lower cutoff frequency of the EMIC wave, the ion composition of the oxygen torus is estimated to be 80.6% H+, 3.4% He+, and 16.0% O+. According to the linearized dispersion relation for EMIC waves, both He+ and O+ ions inhibit EMIC wave growth and the stabilizing effect is stronger for He+ than O+. Therefore, when the H+ fraction or <italic>M</italic> is constant, the denser O+ ions are naturally accompanied by the more tenuous He+ ions, resulting in a weaker stabilizing effect (i.e., larger growth rate). From the Probe B observations, we find that the growth rate becomes larger in the oxygen torus than in the adjacent regions in the plasma trough and the plasmasphere.

DOI： 10.1186/s40623-020-01235-w

Other Link： http://link.springer.com/article/10.1186/s40623-020-01235-w/fulltext.html

K. Shiokawa, M. Nosé, S. Imajo, Y. Tanaka, Y. Miyoshi, K. Hosokawa, M. Connors, M. Engebretson, Y. Kazama, S.‐Y. Wang, S. W. Y. Tam, Tzu‐Fang Chang, Bo‐Jhou Wang, K. Asamura, S. Kasahara, S. Yokota, T. Hori, K. Keika, Y. Kasaba, M. Shoji, Y. Kasahara, A. Matsuoka, I. Shinohara

Journal of Geophysical Research: Space Physics Vol. 125 ( 8 ) 2020.8

Long-Lasting Ground-Satellite High Coherence of Compressional Dayside Pc3-Pc4 Pulsations Reviewed Open Access

Gi-Jeong Kim, Khan-Hyuk Kim, Hyuck-Jin Kwon, Kazuo Shiokawa, Kazue Takahashi, Junga Hwang

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 125 ( 8 ) 2020.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We present observations of broadband (similar to 10-50 mHz) Pc3-Pc4 waves on 4 January 2014. The waves were detected on the dayside simultaneously in a compressional component (delta B-z) at the Radiation Belt Storm Probes A (RBSP-A) in the inner magnetosphere and in the north-south component (delta H) on the ground at a low-latitude Bohyun (BOH) station (L = 1.3) during an interval of small interplanetary magnetic field cone angle, suggesting that upstream ultralow frequency (ULF) waves were the source of the magnetospheric Pc3-Pc4 waves. We observed the ground-satellite high coherence between RBSP-A delta B-z and BOH delta H for a prolonged time interval lasting 6.5hr, which has not been reported previously, during which RBSP-A was on the inbound and outbound legs moving from L = similar to 3.3 to similar to 6.3. In order to understand the spatial mode structure of the compressional waves, we examined the ground-satellite cross phase for the high-coherence interval and found that the waves observed in and out of the plasmasphere propagated earthward at the average fast-mode speed of similar to 700-1,000km/s. We also observed cross-phase values smoothly changing with the radial distance of the spacecraft across the plasmapause. This indicates that the presence of the plasmapause has little effect on our fast-mode waves propagating into the inner magnetosphere and to the ground low-latitude station.

DOI： 10.1029/2020JA028074

The Long-Lasting QP Emissions Observed On Arase Satellite And Lovozero Station Reviewed

V.B. Belakhovsky, K. Shiokawa, A. Matsuoka, Y. Kasahara, I. Shinohara, Y. Miyoshi, S.-Y. Wang, Y. Kazama, S. Kasahara, S. Yokota

2020 XXXIIIrd General Assembly and Scientific Symposium of the International Union of Radio Science 2020.8

Asymmetric Development of Auroral Surges in the Northern and Southern Hemispheres Reviewed Open Access

Uchida H. A., Kataoka R., Kadokura A., Murase K., Yukimatu A. S., Miyoshi Y., Shiokawa K., Ebihara Y., Hosokawa K., Matsuoka A., Kurita S., Fujita S., Shinohara I

GEOPHYSICAL RESEARCH LETTERS Vol. 47 ( 13 ) 2020.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Geophysical Research Letters

Simultaneous eastward and westward traveling surges were observed at Tjörnes, Iceland, and Syowa station, Antarctica, respectively. Several remarkable differences were identified. (1) The position of the initial bright spot was shifted by 1.7 to 2.3 MLT between both hemispheres. (2) The surges differ in traveling speed between the eastward traveling surge (6.5 km s−1) and the westward traveling surge (1.3 km s−1). (3) The Arase satellite was located on a geomagnetic field line connecting both ground stations and observed a significant excess in westward component of the magnetic field, which is consistent with the large shifts of the initial bright spots in both hemispheres. (4) The background Hall current flows eastward (Northern Hemisphere) and westward (Southern Hemisphere). The observed north-south asymmetry of the traveling surges suggests that the ionosphere can play an essential role in controlling the fundamental spatiotemporal development of auroras in both hemispheres.

DOI： 10.1029/2020GL088750

Dilatory and Downward Development of 3-m Scale Irregularities in the Funnel-Like Region of a Rapidly Rising Equatorial Plasma Bubble Reviewed Open Access

S. Tulasi Ram, K. K. Ajith, T. Yokoyama, M. Yamamoto, K. Hozumi, K. Shiokawa, Y. Otsuka, G. Li

Geophysical Research Letters Vol. 47 ( 13 ) 2020.7

Language：English Publishing type：Research paper (scientific journal)

The equatorial plasma bubbles, once developed, grow nonlinearly into topside ionosphere, and simultaneous secondary instabilities lead to the development of shorter scale irregularities. The altitudinal growth and generation of smaller scale irregularities determine the spatio-temporal occurrence and the intensity of ionospheric scintillations at wide spectrum of radio waves and have significant implications on the GNSS/Satellite Based Augmentation Systems. In this letter, we present a unique equatorial plasma bubble observation from equatorial atmosphere radar that provides hitherto undisclosed evidence for the smaller (3-m) scale irregularities initially developing at higher altitudes and subsequently developing to lower altitudes in a narrow funnel-like structure. The responsible mechanisms for early development of shorter scale irregularities in the topside and their subsequent development at lower altitudes are discussed in light of difference between the time scales of altitudinal growth and cascading rate of secondary instabilities through high-resolution bubble model simulations.

DOI： 10.1029/2020GL087256

Severe Magnetic Fluctuations in the Near-Earth Magnetotail: Spectral Analysis and Dependence on Solar Activity Reviewed Open Access

Heqiucen Xu, Kazuo Shiokawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 125 ( 7 ) 2020.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Magnetic fluctuations in the near-Earth magnetotail are an important signature of substorm onset. In a previous statistical study, we reported their occurrence rates, spatial distributions, and relationship with plasma flows. In the present study, we investigated their spectral properties using 11 years of measurements from the Time History of Events and Macroscale Interactions during Substorms mission for 2008-2018. We found 10,848 severe magnetic fluctuation events with sigma(B)/(B) over bar) > 0.5, where sigma(B) and (B) over bar are the standard deviation and average, respectively, of the magnetic field intensity for the local proton gyroperiod. The occurrence rates of severe magnetic fluctuations show no clear dependence on the F-10.7 index in one solar cycle. We extracted 36 dipolarization events with severe magnetic fluctuations. In the power spectral density (PSD) of the magnetic fluctuations during dipolarizations, the steepness of the spectral slope increased with increasing frequency in almost all the events. The average PSDs are shown sorted by (a) distance to the neutral sheet and (b) ambient magnetic field intensity. In all groups, the slopes of the average PSDs increased abruptly from below similar to 10(-1.3) Hz (0.05 Hz) to above similar to 10(-1.3) Hz, which is close to the gyrofrequency of O+ ions. It is the first time that a change of slope near the proton gyrofrequency (frequency range: 0.05-1 Hz) was found in cases of larger ambient magnetic field intensity, implying that the magnetic fluctuations were relatively strong near the proton gyrofrequency. These results suggest that the magnetic fluctuations contribute to the nonmagnetohydrodynamic effect in the ion motion.

DOI： 10.1029/2020JA027834

Modulation of Pc1 Wave Ducting by Equatorial Plasma Bubble Reviewed Open Access

Hyangpyo Kim, Kazuo Shiokawa, Jacheung Park, Yoshizumi Miyoshi, Junga Hwang, Akira Kadokura

GEOPHYSICAL RESEARCH LETTERS Vol. 47 ( 9 ) 2020.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Ducting Pc1 waves are observed over a wide latitudinal range by the low-Earth orbit satellites as compressional mode. In this paper, we present the first observation of the modulation of ducting Pc1 waves by equatorial plasma bubbles (EPBs) based on the Swarm satellites. We show two ducting Pc1 events propagating across EPBs that occurred on 7 April 2016 and on 27 September 2017. We found that the EPBs modulate the Pc1 wave propagation by setting up reflection boundaries and leakage holes in the ionospheric waveguide. We also found that changes of Pc1 wave intensities generally follow the electron density variation and that the intensity is stronger at higher density region. From the comparison between Swarm-A and Swarm-C observations, we conclude that ionospheric plasma plays an important role for Pc1 waveguide even though their density is significantly low in EPBs.

DOI： 10.1029/2020GL088054

Observations of equatorial plasma bubbles using a low-cost 630.0-nm all-sky imager in Ishigaki Island, Japan Reviewed Open Access

Keisuke Hosokawa, Kohei Takami, Susumu Saito, Yasunobu Ogawa, Yuichi Otsuka, Kazuo Shiokawa, Chia-Hung Chen, Chien-Hung Lin

EARTH PLANETS AND SPACE Vol. 72 ( 1 ) 2020.5

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

Here, we introduce a low-cost airglow imaging system developed for observing plasma bubble signatures in 630.0-nm airglow emission from the F region of the ionosphere. The system is composed of a small camera, optical filter, and fish-eye lens, and is operated using free software that automatically records video from the camera. A pilot system was deployed in Ishigaki Island in the southern part of Japan (Lat 24.4, Lon 124.4, Mlat 19.6) and was operated for similar to 1.5 years from 2014 to 2016 corresponding to the recent solar maximum period. The pilot observations demonstrated that it was difficult to identify the plasma bubble signature in the raw image captured every 4 s. However, the quality of the image could be improved by reducing the random noise of instrumental origin through an integration of 30 consecutive raw images obtained in 2 min and further by subtracting the 1-h averaged background image. We compared the deviation images to those from a co-existing airglow imager of OMTIs, which is equipped with a back-illuminated cooled CCD camera with a high quantum efficiency of similar to 90%. It was confirmed that the low-cost airglow imager is capable of imaging the spatial structure of plasma bubbles, including their bifurcating traces. The results of these pilot observations in Ishigaki Island will allow us to distribute the low-cost imager in a wide area and construct a network for monitoring plasma bubbles and their space weather impacts on satellite navigation systems.

DOI： 10.1186/s40623-020-01187-1

Development of low-cost multi-wavelength imager system for studies of aurora and airglow Reviewed Open Access

Y. Ogawa, Y. Tanaka, A. Kadokura, K. Hosokawa, Y. Ebihara, T. Motoba, B. Gustavsson, U. Brändström, Y. Sato, S. Oyama, M. Ozaki, T. Raita, F. Sigernes, S. Nozawa, K. Shiokawa, M. Kosch, K. Kauristie, C. Hall, S. Suzuki, Y. Miyoshi, A. Gerrard, H. Miyaoka, R. Fujii

Polar Science Vol. 23 2020.3

Language：English Publishing type：Research paper (scientific journal)

© 2019 Elsevier B.V. and NIPR This paper introduces a new system that can monitor aurora and atmospheric airglow using a low-cost Watec monochromatic imager (WMI) equipped with a sensitive camera, a filter with high transmittance, and the non-telecentric optics. The WMI system with 486-nm, 558-nm, and 630-nm band-pass filters has observable luminosity of about ~200–4000 Rayleigh for 1.07-sec exposure time and about ~40–1200 Rayleigh for 4.27-sec exposure time, for example. It is demonstrated that the WMI system is capable of detecting 428-nm auroral intensities properly, through comparison with those measured with a collocated electron-multiplying charge-coupled device (EMCCD) imager system with narrower band-pass filter. The WMI system has two distinct advantages over the existing system: One makes it possible to reduce overall costs, and the other is that it enables the continuous observation even under twilight and moonlight conditions. Since 2013 a set of multi-wavelength WMIs has been operating in northern Scandinavia, Svalbard, and Antarctica to study meso- and large-scale aurora and airglow phenomena. Future development of the low-cost WMI system is expected to provide a great opportunity for constructing a global network for multi-wavelength aurora and airglow monitoring.

DOI： 10.1016/j.polar.2019.100501

Multievent Analysis of Oscillatory Motion of Medium-Scale Traveling Ionospheric Disturbances Observed by a 630-nm Airglow Imager Over Tromso Reviewed Open Access

Yadav Sneha, Shiokawa K., Oyama S., Otsuka Y.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 125 ( 3 ) 2020.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

We present a comprehensive investigation on the propagation characteristics of duskside medium-scale traveling ionospheric disturbances (MSTIDs) using 630.0-nm airglow emissions over Tromsø (69.6°N, 19.2°E; magnetic latitude: 66.7°N). The unique points of our observation are (1) duskside MSTIDs primarily exhibited eastward motion under quiet conditions but turned to the westward direction associated with geomagnetic disturbances, (2) the westward moving MSTIDs again turned to the eastward direction when the geomagnetic disturbance ceased, (3) the turning of MSTIDs to the westward direction was invariably associated with an increase of the northward component of the magnetic field observed by the local ground-based magnetometers and with the equatorward expansion of the auroral oval, and (4) the Super Dual Auroral Radar Network convection maps revealed that the location of Tromsø was inside (outside) the duskside convection cell during the time of appearance of westward (eastward) moving MSTIDs. The average eastward and westward velocities of MSTIDs were ~25–80 and ~40–140 m/s, respectively. The Doppler shift measurement of the 630-nm airglow by a Fabry-Perot interferometer at Tromsø showed that northeastward winds were predominant during the appearance of eastward moving MSTIDs. These experimental evidences suggest that the oscillatory motion of MSTIDs over high latitudes is driven by the convection electric field. The MSTIDs tend to move eastward under geomagnetically quiet conditions but show westward motion under the influence of convection electric field associated with auroral activities in the duskside of two-cell convection pattern.

DOI： 10.1029/2019JA027598

Fine-Scale Visualization of Aurora in a Wide Area Using Color Digital Camera Images From the International Space Station Reviewed Open Access

Sota Nanjo, Yuta Hozumi, Keisuke Hosokawa, Ryuho Kataoka, Yoshizumi Miyoshi, Shin-ichiro Oyama, Mitsunori Ozaki, Kazuo Shiokawa, Satoshi Kurita

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 125 ( 3 ) 2020.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

The full-color photographs of aurora have been taken with digital single-lens reflex cameras mounted on the International Space Station (ISS). Since these photographs do not have accurate time and geographical information, in order to use them as scientific data, it is necessary to calibrate the imaging parameters (such as looking direction and angle of view of the camera) of the photographs. For this purpose, we calibrated the imaging parameters using a city light image taken from the Defense Meteorological Satellite Program satellite following the method of Hozumi et al. (2016, https://doi.org/10.1186/s40623-016-0532-z). We mapped the photographs onto the geographic coordinate system using the calibrated imaging parameters. To evaluate the accuracy of the mapping, we compared the aurora taken simultaneously from ISS and ground. Comparing the spatial structure of discrete aurora and the temporal variation of pulsating aurora, the accuracy of the data set is less than 0.3 s in time and less than 5 km in space in the direction perpendicular to the looking direction of the camera. The generated data set has a wide field of view (similar to 1,100 x 900 km), and their temporal resolution is less than 1 s. Not only that, the field of view can sweep a wide area (similar to 3,000km in longitude) in a short time (similar to 10 min). Thus, this new imaging capability will enable us to capture the evolution of fine-scale spatial structure of aurora in a wide area.

DOI： 10.1029/2019JA027729

Equatorial Plasma Bubble Zonal Drift Velocity Variations in Response to Season, Local Time, and Solar Activity across Southeast Asia Reviewed

Sarudin I., Hamid N. S. A., Abdullah M., Buhari S. M., Shiokawa K., Otsuka Y., Yatini C. Y.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 125 ( 3 ) 2020.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

This work investigated the zonal drift velocity, VE, of equatorial plasma bubbles (EPBs) which was calculated from the zonal keogram of the rate of total electron content index obtained using the Global Positioning System data from the Malaysia Real-Time Kinematics GNSS Network over Southeast Asia across the period 2008 until 2013 (498 nights). In general, a long-term study on the VE of EPBs and its dependence on the season, local time, and solar activity over Southeast Asia by using Global Positioning System multipoint receivers has never been conducted before. The case study showed that the VE estimated from Malaysia Real-Time Kinematics GNSS Network was basically within a similar range to that of the 630-nm airglow images obtained at Kototabang, Indonesia. Furthermore, the VE of EPBs was higher during high solar-activity period, which was in line with past studies. The time range of the EPB VE peak is more accurately determined compared to previous studies. In high solar activity conditions, a peak of VE was observed at 2130 LT (equinox), 2200 LT (June solstice), and after 2300 LT (December solstice). After this peak, the EPB VE steadily decreased with time during the equinox and was varied throughout the night during June solstice. Moreover, it was found to differ with time from the evening to the postmidnight period during December solstice.

DOI： 10.1029/2019JA027521

ULF Modulation of Energetic Electron Precipitations Observed by VLF/LF Radio Propagation Invited Reviewed

Takuya Miyashita, Hiroyo Ohya, Fuminori Tsuchiya, Asuka Hirai, Mitsunori Ozaki, Kazuo Shiokawa, Yoshizumi Miyoshi, Nozomu Nishitani, Mariko Teramoto, Martin Connors, Simon G. Shepherd, Yoshiya Kasahara, Atsushi Kumamoto, Masafumi Shoji, Iku Shinohara, Hiroyuki Nakata, Toshiaki Takano

Radio Science Bulletin 2020.3

Wavenumber Spectra of Atmospheric Gravity Waves and Medium-Scale Traveling Ionospheric Disturbances Based on More Than 10-Year Airglow Images in Japan, Russia, and Canada Reviewed Open Access

Satoshi Tsuchiya, Kazuo Shiokawa, Yuichi Otsuka, Takuji Nakamura, Mamoru Yamamoto, Martin Connors, Ian Schofield, Boris Shevtsov, Igor Poddelsky

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 125 ( 3 ) 2020.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We have studied atmospheric gravity waves (AGWs) and nighttime medium-scale traveling ionospheric disturbances (MSTIDs) by applying three-dimensional spectral analysis technique to 557.7- and 630.0-nm airglow images at Shigaraki (SGK) (35 degrees N, 136 degrees E, 1999-2017) and Rikubetsu (RIK) (44 degrees N, 144 degrees E, 1999-2017), Japan, Athabasca (ATH), Canada, (55 degrees N, 247 degrees E, 2005-2017), and Magadan (MGD), Russia (60 degrees N, 151 degrees E, 2008-2017), focusing on their horizontal wavenumber spectra. For the AGWs in 557.7-nm images, the power spectra in summer are stronger than in other seasons, probably due to stronger tropospheric convection. The highest energy content of the waves are mostly at wavelengths between 20 and 300 km at MGD, ATH, and RIK, while it is above 200 km at SGK. The largest power spectral density is obtained at RIK at wavelengths of 30-100 km and then ATH. The slopes of the horizontal wavenumber spectra varies from -2.77 to -3.22. From the MSTIDs in 630.0-nm images, the power spectra in summer at RIK and SGK are stronger than those in other seasons regardless of solar activity. The power spectra in solar quiet time are stronger than those in solar active time at all four stations. These features can be explained by the Perkins instability with coupling between sporadic E and F layers. The spectral slope decreases with increasing latitudes. Weak positive correlations were obtained between the daily wave power of AGWs in 557.7-nm images and MSTIDs in 630.0-nm images, suggesting that the MSTIDs in the thermosphere may be partially generated by the AGWs from the mesopause region.Plain Language Summary In this paper we study atmospheric gravity waves (AGWs) and nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed at four stations in Japan, Canada, and Russia, in 557.7- and 630.0-nm airglow images over more than 10 years. The 557.7-nm airglow has an emission layer at altitudes of 90-100 km (mesopause region). The waves seen in the 557.7-nm airglow images mainly indicates AGWs. The 630.0-nm airglow has an emission layer at altitudes of 200-300 km (bottomside ionosphere). The waves seen in the 630.0-nm airglow images mainly indicates MSTIDs in the ionosphere. The AGWs in the mesopause region are the main driver of global atmospheric circulation in the middle atmosphere. The MSTIDs in the bottomside ionosphere are one of the causes of the satellite positioning error. We show typical energy content, propagation direction, and wavelengths of these waves at these two altitudes and discuss possible reason of the observed characteristics. These results contribute to our understanding of generation and propagation of AGWs and MSTIDs in the upper atmosphere.

DOI： 10.1029/2019JA026807

Multiple time-scale beats in aurora: precise orchestration via magnetospheric chorus waves Reviewed Open Access

Hosokawa K., Miyoshi Y., Ozaki M., Oyama S- I, Ogawa Y., Kurita S., Kasahara Y., Kasaba Y., Yagitani S., Matsuda S., Tsuchiya F., Kumamoto A., Kataoka R., Shiokawa K., Raita T., Turunen E., Takashima T., Shinohara I, Fujii R.

SCIENTIFIC REPORTS Vol. 10 ( 1 ) page： 3380 2020.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Scientific reports

The brightness of aurorae in Earth's polar region often beats with periods ranging from sub-second to a few tens of a second. Past observations showed that the beat of the aurora is composed of a superposition of two independent periodicities that co-exist hierarchically. However, the origin of such multiple time-scale beats in aurora remains poorly understood due to a lack of measurements with sufficiently high temporal resolution. By coordinating experiments using ultrafast auroral imagers deployed in the Arctic with the newly-launched magnetospheric satellite Arase, we succeeded in identifying an excellent agreement between the beats in aurorae and intensity modulations of natural electromagnetic waves in space called "chorus". In particular, sub-second scintillations of aurorae are precisely controlled by fine-scale chirping rhythms in chorus. The observation of this striking correlation demonstrates that resonant interaction between energetic electrons and chorus waves in magnetospheres orchestrates the complex behavior of aurora on Earth and other magnetized planets.

DOI： 10.1038/s41598-020-59642-8

Probing afternoon detached aurora and high-latitude trough based on DMSP observations Reviewed Open Access

Su Zhou, Kazuo Shiokawa, Igor Poddelsky, Yuqing Chen, Jin Zhang

ADVANCES IN SPACE RESEARCH Vol. 65 ( 1 ) page： 214 - 220 2020.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

The present work displays the observations of an afternoon detached aurora along with ionospheric high-latitude trough. The event was observed by DMSP F17 on 19 September 2014. The afternoon detached aurora was isolated from the auroral oval and was located between 12:00-18:00 magnetic local time (MLT) and 65-70 degrees geomagnetic latitude (MLAT). Particle observations indicate that the afternoon detached aurora was produced by energetic ring current ions with energies above similar to 10 keV where the main ion energy was likely to be above the upper limit of DMSP measurement (similar to 30 keV). Magnetometer observation from the ground implies that the energetic ions were likely scattered by EMIC waves. Both the detached aurora and the auroral oval are found to be well inside the high-latitude trough with MLAT between similar to 64 degrees and similar to 76 degrees (68-80 degrees GLAT). The auroral oval corresponds to a westward (sunward) plasma drift. It is expected that the westward drift transports the low-density plasma in the nightside toward the dayside, leading to the high-latitude trough formation. The afternoon detached aurora was well equatorward of the high-latitude trough, and the corresponding plasma drift was nearly zero. The plasma associated with the detached aurora is expected to be stagnant, and broaden the high-latitude trough equatorward. (C) 2019 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.asr.2019.10.003

Conjugate Observations of Dayside and Nightside VLF Chorus and QP Emissions Between Arase (ERG) and Kannuslehto, Finland Reviewed Open Access

Claudia Martinez-Calderon, Yuto Katoh, Jyrki Manninen, Yoshiya Kasahara, Shoya Matsuda, Atsushi Kumamoto, Fuminori Tsuchiya, Ayako Matsuoka, Masafumi Shoji, Mariko Teramoto, Iku Shinohara, Kazuo Shiokawa, Yoshizumi Miyoshi

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 125 ( 1 ) 2020.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We compare for the first time two conjugate events showing simultaneous very low frequency (VLF) wave observations between the same ground station and spacecraft, at different geomagnetic conditions and on opposite sides of the magnetosphere. Waves were observed at Kannuslehto (MLAT = 64.4 degrees N, L = 5.46), Finland, and on board Arase (Exploration of energization and Radiation in Geospace, ERG) in the inner magnetosphere. Case 1 on 28 March 2017 shows quasiperiodic (QP) emissions and chorus simultaneously observed on the postmidnight side during the recovery phase of a storm, with sustained high solar wind speed and AE index. Case 2 on 30 November 2017 shows clear one-to-one correspondence of QP elements on the noonside during geomagnetic quiet time (Dst > 10 nT and AE < 100 nT). We present the characteristics of both cases, focusing on coherence and spatial extent of the waves, electron density, and magnetic field variations. We report that the magnetic field gradient plays a role in the changes of spectral features of the waves.

DOI： 10.1029/2019JA026663

Capability of Geomagnetic Storm Parameters to Identify Severe Space Weather Reviewed Open Access

Balan N., Zhang Qing-He, Xing Zanyang, Skoug R., Shiokawa K., Luehr H., Ram S. Tulasi, Otsuka Y., Zhao Lingxin

ASTROPHYSICAL JOURNAL Vol. 887 ( 1 ) 2019.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Astrophysical Journal

The paper investigates the capability of geomagnetic storm parameters in the disturbance storm-time (Dst), Kp, and AE indices to distinguish between severe space weather (SvSW) that causes the reported electric power outages and/or telecommunication failures and normal space weather (NSW) that does not cause these severe effects in a 50 yr period (1958-2007). The parameters include the storm intensities DstMin (minimum Dst during the main phase, MP, of the storm), (dDst/dt)MPmax, Kpmax, and AEmax. In addition, the impulsive parameter is derived for the storms that are automatically identified in the Kyoto Dst and USGS Dst.∫TMP| DstMP| dt is the integral of the modulus of the Dst from onset of the MP (MPO) to the DstMin. T MP is the MP duration from MPO to DstMin. The corresponding mean values KpMP and AEMP are also calculated. Regardless of the significant differences in the storm parameters between the two Dst indices, the IpsDst in both indices seems to identify four of the five SvSW events (and the Carrington event) in more than 750 NSW events that have been reported to have occurred in 1958-2007, while all other parameters separate one or two SvSWs from the NSWs. Using the Kyoto IpsDst threshold of -250 nT, we demonstrate a 100% true SvSW identification rate with only one false NSW. Using the false NSW event (1972 August 4), we investigate whether using a higher resolution Dst might result in a more accurate identification of SvSWs. The mechanism of the impulsive action leading to large IpsDst and SvSW involves the coincidence that the fast interplanetary coronal mass ejection velocity V contains its shock (or front) velocity ΔV and large interplanetary magnetic field Bz southward covering ΔV.

DOI： 10.3847/1538-4357/ab5113

A Neural Network-Based Ionospheric Model Over Africa From Constellation Observing System for Meteorology, Ionosphere, and Climate and Ground Global Positioning System Observations Reviewed

Daniel Okoh, Gopi Seemala, Babatunde Rabiu, John Bosco Habarulema, Shuanggen Jin, Kazuo Shiokawa, Yuichi Otsuka, Malini Aggarwal, Jean Uwamahoro, Patrick Mungufeni, Bolaji Segun, Aderonke Obafaye, Nada Ellahony, Chinelo Okonkwo, Mpho Tshisaphungo, Dadaso Shetti

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 124 ( 12 ) page： 10512 - 10532 2019.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

The first regional total electron content (TEC) model over the entire African region (known as AfriTEC model) using empirical observations is developed and presented. Artificial neural networks were used to train TEC observations obtained from Global Positioning System receivers, both on ground and onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate satellites for the African region from years 2000 to 2017. The neural network training was implemented using inputs that enabled the networks to learn diurnal variations, seasonal variations, spatial variations, and variations that are connected with the level of solar activity, for quiet geomagnetic conditions (-20 nT <= Dst <= 20 nT). The effectiveness of three solar activity indices (sunspot number, solar radio flux at 10.7-cm wavelength [F10.7], and solar ultraviolet [UV] flux at 1 AU) for the neural network trainings was tested. The F10.7 and UV were more effective, and the F10.7 was used as it gave the least errors on the validation data set used. Equatorial anomaly simulations show a reduced occurrence during the June solstice season. The distance of separation between the anomaly crests is typically in the range from about 11.5 +/- 1.0 degrees to 16.0 +/- 1.0 degrees. The separation is observed to widen as solar activity levels increase. During the December solstice, the anomaly region shifts southwards of the equinox locations; in year 2012, the trough shifted by about 1.5 degrees and the southern crest shifted by over 2.5 degrees.

DOI： 10.1029/2019JA027065

Longitudinal Extent of Magnetospheric ELF/VLFWaves using Multipoint PWING Ground Stations at Subauroral Latitudes Reviewed Open Access

Yuhei Takeshita, Kazuo Shiokawa, Mitsunori Ozaki, Jyrki Manninen, Shin-Ichiro Oyama, Martin Connors, Dmitry Baishev, Vladimir Kurkin, Alexey Oinats

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 124 ( 12 ) page： 9881 - 9892 2019.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Magnetospheric extremely low frequency/very low frequency (ELF/VLF) waves are plasma waves emitted from high-energy electrons in the magnetosphere. These waves have received much attention, as they contribute to the acceleration and loss of relativistic electrons in the radiation belts through wave-particle interactions. The longitudinal extent of ELF/VLF waves has not been well-understood, although the extent is important in quantitative evaluation of relativistic electron variations. In this study, we analyzed data from continuous ground-based simultaneous observations of ELF/VLF waves over a 2-month period in November and December of 2017, using six loop antennas located at roughly equal intervals around the north geomagnetic pole at similar to 60 degrees. magnetic latitudes. We estimated the longitudinal extent of magnetospheric ELF/VLF waves based on their occurrence rate. Our results showed that the ELF/VLF wave occurrence rate differed by twofold to threefold, depending on the longitudes of the observation sites. We explain this difference in terms of longitudinal differences in the ionosphere's magnetic field intensity, possibly due to the electron loss that occurs during the bounce motion at longitudes of small magnetic field intensity. Based on our statistical analysis, we estimated the typical longitudinal extent of ELF/VLF waves as similar to 76 degrees. Time series analysis results showed that the large longitudinal extent of the ELF/VLF waves occurs frequently during the main phase of geomagnetic storms and is also associated with substorms represented by the auroral electrojet index.

DOI： 10.1029/2019JA026810

Three Different Episodes of Prompt Equatorial Electric Field Perturbations Under Steady Southward IMF Bz During St. Patrick's Day Storm Reviewed

S. Tulasi Ram, B. Nilam, N. Balan, Q. Zhang, K. Shiokawa, D. Chakrabarty, Z. Xing, K. Venkatesh, B. Veenadhari, A. Yoshikawa

Journal of Geophysical Research: Space Physics Vol. 124 ( 12 ) page： 10428 - 10443 2019.12

Language：English Publishing type：Research paper (scientific journal)

Three different episodes of prompt penetration electric field (PPEF) disturbances are observed during the main phase of the St. Patrick's Day storm on 17 March 2015 under steady southward interplanetary magnetic field (IMF) Bz conditions unlike the conventional PPEF associated with southward or northward turnings of IMF Bz. These PPEF events took place during the period when strong disturbance dynamo fields are prevailing in the background. The first event is triggered by a solar wind dynamic pressure pulse that caused a sharp eastward PPEF and strong enhancement of equatorial electrojet current in Brazilian dayside. The second event caused another short but strong westward PPEF on dayside due to the reversal of IMF By from duskward to dawnward under steady IMF Bz. The third event caused a longer eastward PPEF in association with a solar wind dynamic pressure pulse followed by the onset of a substorm, which has led to strong enhancement of equatorial electrojet, quick rejuvenation and symmetric redistribution of equatorial ionization anomaly in the Brazilian sector. The signatures of the PPEF with opposite polarity and smaller magnitudes are also observed in the Asian sector on the nightside. The possible mechanisms for the observed PPEF events under steady IMF Bz are discussed in terms of changes in the high-latitude field-aligned currents and reconfiguration of high-latitude convection fields using Active Magnetosphere and Planetary Electrodynamics Response Experiment and Super Dual Auroral Radar Network high-frequency radar observations.

DOI： 10.1029/2019JA027069

IpsDst of Dst Storms Applied to Ionosphere-Thermosphere Storms and Low-Latitude Aurora Reviewed

Balan N., Zhang Qing -He, Shiokawa K., Skoug R., Xing Zanyang, Ram S. Tulasi, Otsuka Y.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 124 ( 11 ) page： 9552 - 9565 2019.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

Conventionally, the minimum value of Dst (DstMin) and maximum values of Kp and AE (Kpmax and AEmax) representing the geomagnetic storm intensities have been used for investigating space weather in Earth's environment. The present paper uses the derived parameters (IpsDst, IpsKp, and IpsAE) giving the mean values of Dst, Kp, and AE during the main phase (MP) of Dst storms for investigating ionosphere-thermosphere storms and low-latitude (630 nm) aurora. The derived parameters (IpsDst, IpsKp, and IpsAE) representing the impulsive strength of geomagnetic storms seem to have more systematic dependence among themselves than among the intensities (DstMin, Kpmax, and AEmax). The ionosphere-thermosphere storms observed by the CHAMP (Challenging Minisatellite Payload) satellite and low-latitude auroras observed by optical imagers are much more intense during high impulsive storms than high intensity storms. In a statistical sense, over 175 positive ionospheric storms (△NmF2) observed in 1985–2005 and the intensity of 20 red auroras observed in 1989–2004 at midlatitudes correlate better with the impulsive parameters than the intensity parameters, with the best correlation being with IpsDst. The mechanism of the impulsive action (high-energy input over a short duration) leading to large IpsDst arises from the impact of fast solar storms (interplanetary coronal mass ejections) with large IMF Bz southward at their front (or shock). The impulsive action results in bright low-latitude auroras and strong ionosphere-thermosphere storms.

DOI： 10.1029/2019JA027080

Statistical Study of Auroral/Resonant-Scattering 427.8-nm Emission Observed at Subauroral Latitudes Over 14 Years Reviewed

Shiokawa K., Otsuka Y., Connors M.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 124 ( 11 ) page： 9293 - 9301 2019.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

Auroral emission at 427.8-nm from N2+ ions is caused by precipitation of energetic electrons, or by resonant scattering of sunlight by auroral N2+ ions. The latter often causes impressive purple aurora at high altitudes. However, statistical characteristics of auroral 427.8-nm emission have not been well studied. In this paper we report occurrence characteristics of high 427.8-nm emission intensities (more than 100 R) at subauroral latitudes, based on measurements by a filter-tilting photometer over 14 years (2005–2018) at Athabasca, Canada (magnetic latitude: ~62°). We divided the data set into solar elevation angles (θs) more than and less than −24° (shadow height of sunlight: 600 km) to separate the 427.8-nm emissions caused by resonant scattering of sunlight and those excited by auroral electrons, respectively. The occurrence rate of 427.8-nm emissions of more than 100 R is 10.6% and 7.65% for θs more than and less than −24°, respectively, confirming that resonant scattering of sunlight by N2+ ions is a cause of the strong 427.8-nm emissions of more than 100 R in the sunlit ionosphere. The occurrence rate is high in the postmidnight sector and increases with increasing geomagnetic activity, solar wind speed, and density. The occurrence rate is lowest in winter. A high occurrence rate was observed in 2015–2018, during the declining phase of the 11-year solar activity. Superposed epoch analysis indicates that the 427.8-nm emission exceeds 100 R when solar wind speed increases and solar wind density concurrently decreases, though the standard deviation of the data is rather large.

DOI： 10.1029/2019JA026704

High-latitude thermospheric wind study using a Fabry-Perot interferometer at Tromso in Norway: averages and variations during quiet times Reviewed Open Access

Heqiucen Xu, Kazuo Shiokawa, Shin-ichiro Oyama, Satonori Nozawa

EARTH PLANETS AND SPACE Vol. 71 ( 1 ) 2019.10

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGEROPEN

The average winds in the thermosphere during geomagnetically quiet times are important because they provide a baseline wind in the upper atmosphere, but they remain insufficiently understood at high latitudes. This paper reports the first direct ground-based wind measurements of the quiet-time thermospheric wind pattern at Tromso in Norway using 2009-2015 data from a Fabry-Perot interferometer. We analyzed red-line wind measurements (630.0 nm; altitude: 200-300 km). On average, the zonal wind shows a decrease of eastward wind compared with diurnal tidal wind before midnight. A maximum speed of 100 m/s occurs at both the dusk and dawn sides. The meridional wind has a diurnal tide structure with a minimum value of - 130 m/s around midnight. We also found occasional large wind deviations (> 100 m/s) from the averages, even during geomagnetically quiet times. We suggest that these large wind deviations are caused by the plasma convection associated with weak substorm activities with auroral electrojet (AE) index values of less than 100 nT that occurred at local times different from that at Tromso.

DOI： 10.1186/s40623-019-1093-8

Three-Dimensional Fourier Analysis of the Phase Velocity Distributions of Mesospheric and Ionospheric Waves Based on Airglow Images Collected Over 10 Years: Comparison of Magadan, Russia, and Athabasca, Canada Reviewed Open Access

Direct comparison between magnetospheric plasma waves and polar mesosphere winter echoes in both hemispheres Reviewed International journal Open Access

Tanaka, Y.-M, T. Nishiyama, A. Kadokura, M. Ozaki, K. Shiokawa, S. Oyama, M. Nosé, T. Nagatsuma, M. Tsutsumi, K. Nishimura, K. Sato, Y. Miyoshi, Y. Kasahara, A. Kumamoto, F. Tsuchiya, M. Hikishima, S. Matsuda, A. Matsuoka, M. Shinohara, A. Fujimoto, M. Teramoto, R. Nomura, R. Kataoka, A. Sessai Yukimatu

J. Geophys. Res. (SPA) Vol. 124 ( 11 ) page： 9626 - 9639 2019.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AGU (Wiley)

We present the first and direct comparison between magnetospheric plasma waves and polar mesosphere winter echoes (PMWE) simultaneously observed by the conjugate observation with Arase satellite and high‐power atmospheric radars in both hemispheres, namely, the Program of the Antarctic Syowa Mesosphere, Stratosphere, and Troposphere/Incoherent Scatter Radar at Syowa Station (SYO; −69.00°S, 39.58°E), Antarctica, and the Middle Atmosphere Alomar Radar System at Andøya (AND; 69.30°N, 16.04°E), Norway. The PMWE were observed during 03–07 UT on 21 March 2017, just after the arrival of corotating interaction region in front of high‐speed solar wind stream. An isolated substorm occurred at 04 UT during this interval. Electromagnetic ion cyclotron (EMIC) waves and whistler mode chorus waves were simultaneously observed near the magnetic equator and showed similar temporal variations to that of the PMWE. These results indicate that chorus waves as well as EMIC waves are drivers of precipitation of energetic electrons, including relativistic electrons, which make PMWE detectable at 55‐ to 80‐km altitude. Cosmic noise absorption measured with a 38.2‐MHz imaging riometer and low‐altitude echoes at 55–70 km measured with an medium‐frequency radar at SYO also support the relativistic electron precipitation. We suggest a possible scenario in which the various phenomena observed in near‐Earth space, such as magnetospheric plasma waves (EMIC waves and chorus waves), pulsating auroras, cosmic noise absorption, and PMWE, can be explained by the interaction between the high‐speed solar wind containing corotating interaction regions and the magnetosphere.

DOI： 10.1029/2019JA026891

Satoshi Tsuchiya, Kazuo Shiokawa, Hatsuki Fujinami, Yuichi Otsuka, Takuji Nakamura, Martin Connors, Ian Schofield, Boris Shevtsov, Igor Poddelskiy

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 124 ( 10 ) page： 8110 - 8124 2019.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We studied atmospheric gravity waves (AGWs) and nighttime medium-scale traveling ionospheric disturbances (MSTIDs) using a three-dimensional spectral analysis technique for airglow images at wavelengths of 557.7 nm (altitude: 90-100 km for AGWs) and 630.0 nm (200-300 km for MSTIDs), obtained from Athabasca (ATH), Canada (55 degrees N, 247 degrees E, 2005-2017), and Magadan (MGD), Russia (60 degrees N, 151 degrees E, 2008-2017), over 10-13 years. The AGW propagation direction in summer was from northwestward to northward in ATH and northeastward in MGD with phase speeds of 20-60 m/s. In winter at ATH, they are more omnidirectional with weak preference from northwestward to southward with a speed less than 40 m/s, while another weaker power exists from northeastward to southeastward from 70 to 120 m/s. In winter at MGD, there was no dominant direction in the phase-velocity spectra with spectral power an order smaller than ATH. We suggest that these AGW characteristics were caused by wind filtering and intensity and locations of tropospheric sources. The MSTIDs at ATH propagated southwestward in spring and winter and northeastward in summer and fall. The MSTIDs at MGD propagated northeastward, eastward, and westward in spring, fall, and winter, respectively, with weaker power than that at ATH. The phase speeds are mostly less than 100 m/s except for fall. The propagation direction tends to change from south-southwestward in the evening to north-northeastward after the midnight at both ATH and MGD. We discuss possible reasons for these MSTID characteristics at high latitudes based on Perkins and E-F coupling instabilities, high-latitude plasma convection, and thermospheric neutral winds.

DOI： 10.1029/2019JA026783

Mesoscale Convection Structures Associated With Airglow Patches Characterized Using Cluster-Imager Conjunctions Reviewed Open Access

Goodwin L. V, Nishimura Y., Zou Y., Shiokawa K., Jayachandran P. T.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 124 ( 9 ) page： 7513 - 7532 2019.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

Polar cap ionospheric plasma flow studies often focus on large-scale averaged properties and neglect the mesoscale component. However, recent studies have shown that mesoscale flows are often found to be collocated with airglow patches. These mesoscale flows are typically a few hundred meters per second faster than the large-scale background and are associated with major auroral intensifications when they reach the poleward boundary of the nightside auroral oval. Patches often also contain ionospheric signatures of enhanced field-aligned currents and localized electron flux enhancements, indicating that patches are associated with magnetosphere-ionosphere coupling on open field lines. However, magnetospheric measurements of this coupling are lacking, and it has not been understood what the magnetospheric signatures of patches on open field lines are. The work presented here explores the magnetospheric counterpart of patches and the role these structures have in plasma transport across the open field-line region in the magnetosphere. Using red-line emission measurements from the Resolute Bay Optical Mesosphere Thermosphere Imager, and magnetospheric measurements made by the Cluster spacecraft, conjugate events from 2005 to 2009 show that lobe measurements on field lines connected to patches display (1) electric field enhancements, (2) Region 1 sense field-aligned currents, (3) field-aligned enhancements in soft electron flux, (4) downward Poynting fluxes, and (5) in some cases enhancements in ion flux, including ion outflows. These observations indicate that patches highlight a localized fast flow channel system that is driven by the magnetosphere and propagates from the dayside to the nightside, most likely being initiated by enhanced localized dayside reconnection.

DOI： 10.1029/2019JA026611

Thermospheric wind variations observed by a Fabry-Perot interferometer at Tromso, Norway, at substorm onsets Reviewed Open Access

Heqiucen Xu, Kazuo Shiokawa, Shin-ichiro Oyama, Yuichi Otsuka

EARTH PLANETS AND SPACE Vol. 71 ( 1 ) 2019.8

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGEROPEN

Energy input from the magnetosphere during substorms can strongly affect the high-latitude thermosphere. The ionospheric current caused by thermospheric wind variations may also provide a feedback to the magnetosphere. In this study, we investigate the characteristics of high-latitude thermospheric wind variations at local substorm onsets at Tromso, Norway, as well as the possibility of such feedback mechanism. A Fabry-Perot interferometer (FPI) at Tromso provided wind measurements estimated from the Doppler shift of red-line emission (630.0 nm) of aurora and airglow. We analyzed wind data in 2009 with a time resolution of similar to 13 min. We first carefully identified the onset times of isolated local substorms at Tromso and extracted four wind measurements from red-line emission. All these events showed increases of eastward components at local substorm onsets. For northward components, these events showed decreases except for those at midnight. The observed wind variations at local substorm onsets were less than 49 m/s. These values are much smaller than the typical plasma convection speed in the auroral zone. We speculate that the ionospheric current caused by thermospheric wind variations at local substorm onsets does not provide strong feedback to the development of substorm expansion phase in the magnetotail. We discuss the possible causes of these wind variations in the context of plasma convection, diurnal tides, and arc-associated electric field.

DOI： 10.1186/s40623-019-1072-0

Multi-instrument Observation of Nonlinear EMIC-Driven Electron Precipitation at sub-MeV Energies Reviewed

Hendry A. T., Santolik O., Kletzing C. A., Rodger C. J., Shiokawa K., Baishev D.

GEOPHYSICAL RESEARCH LETTERS Vol. 46 ( 13 ) page： 7248 - 7257 2019.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Geophysical Research Letters

In recent years, experimental results have consistently shown evidence of electromagnetic ion cyclotron (EMIC) wave-driven electron precipitation down to energies as low as hundreds of keV. However, this is at odds with the limits expected from quasi-linear theory. Recent analysis using nonlinear theory has suggested energy limits as low as hundreds of keV, consistent with the experimental results, although to date this has not been experimentally verified. In this study, we present concurrent observations from Polar-orbiting Operational Environmental Satellite, Radiation Belt Storm Probes, Global Positioning System, and ground-based instruments, showing concurrent EMIC waves and sub–MeV electron precipitation, and a global dropout in electron flux. We show through test particle simulation that the observed waves are capable of scattering electrons as low as hundreds of keV into the loss cone through nonlinear trapping, consistent with the experimentally observed electron precipitation.

DOI： 10.1029/2019GL082401

EMIC waves converted from equatorial noise due to M/Q=2 ions in the plasmasphere: Observations from Van Allen Probes and Arase Reviewed Open Access

Miyoshi, Y, S. Matsuda, S. Kurita, K. Nomura, K. Keika, M. Shoji, N. Kitamura, Y. Kasahara, A. Matsuoka, I. Shinohara, K. Shiokawa, S. Machida, O. Santolik, S. A. Boardsen, R. B. Horne, J. F. Wygant

Geophys. Res. Lett. Vol. 46 ( 11 ) page： 5662 - 5669 2019.6

Comprehensive Study of Low-Latitude Pi2 Pulsations Using Observations From Multisatellite Swarm Mission and Global Network of Ground Observatories Reviewed Open Access

Neethal Thomas, Kazuo Shiokawa, Geeta Vichare

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 124 ( 3 ) page： 1966 - 1991 2019.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

To understand the spatial features of low-latitude Pi2 (6.6-25 mHz) pulsations, a comprehensive study is carried out for the first time using magnetic field measurements from a global network of low-latitude ground stations (Mlat: +/- 2 degrees - 51 degrees) and the Swarm multisatellites located simultaneously at day and night local times. We have investigated 1-year data from 2014 and found 15 Pi2 events with coherent oscillations at satellite and ground. The Pi2 oscillations in the compressional, toroidal, and poloidal components at satellite and H, D, and Z components at ground are investigated by estimating its coherence, amplitude, and cross phase with respect to midnight ground H variations. The analogous pairs of magnetic field components (satellite compressional with ground H and satellite toroidal with ground D) above and below the ionosphere are found to have identical phase during night and opposite phase during day, indicating the magnetospheric and ionospheric sources for nighttime and daytime Pi2s, respectively. During nighttime, Pi2 oscillations identified in the poloidal component are found to oscillate in phase (out of phase) in the Southern (Northern) Hemisphere. At ground, the phase and amplitude of H showed significant change near the dawn terminator, whereas H oscillates mostly in phase with respect to midnight ground H at other local times. The oscillations in D component have phase reversal near midnight, dawn, dusk, and noon meridians with opposite hemispheres having opposite phase. These Pi2 characteristics observed globally at ground and at the topside ionosphere suggest that the sources for nighttime and daytime low-latitude Pi2s are oscillating field-aligned currents and ionospheric currents, respectively.

DOI： 10.1029/2018JA026094

Observations of low-latitude travelling ionospheric disturbances by a 630.0-nm airglow imager and the CHAMP satellite over Indonesia Reviewed International journal Open Access

A. C. Moral, K. Shiokawa, S. Suzuki, Huixin Liu, Y. Otsuka, C. Y. Yatini

J. Geophys. Res. Vol. 124 ( 3 ) page： 2198 - 2212 2019.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report the first comparison of ground and satellite measurements of low-latitude traveling ionospheric disturbances (TIDs). Three TID events were simultaneously observed by a 630.0-nm airglow imager and the CHAllenging Minisatellite Payload (CHAMP) satellite at Kototabang, Indonesia (geographic coordinates: 0.2 degrees S, 100.3 degrees E, geomagnetic latitude: 10.6 degrees S). In 630.0-nm airglow images of all three events, there are clear southward-moving structures. Events 1 and 2 are a single pulse with horizontal scales of similar to 500-1,000 km. Event 3 shows five wave fronts with a horizontal scale size of 500-1,000 km. All three TIDs are medium-scale TIDs. Horizontal wavelengths of both airglow intensity at an average emission altitude of 250 km and CHAMP neutral density variations measured at 400 km are estimated by fitting a sinusoidal function to the observed data. The estimated horizontal wavelengths for airglow and neutral density data are 1,031 and 880 km for event 1 and 560 and 420 km for event 3, respectively. These values between airglow and CHAMP are comparable, suggesting both instruments are observing the same wave. For event 1, the CHAMP electron density mapped along the geomagnetic field line onto the airglow altitude does not show wave structure similar to the airglow variation. For events 2 and 3, the plasma density did not show wavy structures similar to the waves seen in the airglow image and CHAMP neutral density. These results suggest that the TIDs observed in airglow images are not caused by ionospheric plasma instability but by gravity waves in the thermosphere.

DOI： 10.1029/2018JA025634

Spatial Gradients in Geomagnetic Storm Time Currents Observed by Swarm Multispacecraft Mission Reviewed Open Access

Vichare Geeta, Thomas Neethal, Shiokawa Kazau, Bhaskar Ankush, Sinha Ashwini Kumar

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 124 ( 2 ) page： 982 - 995 2019.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

This paper presents a comprehensive study of geomagnetic storm time currents using magnetic field recorded by multispacecraft polar-orbiting mission, Swarm. During geomagnetic storm period, the magnetic field variations obtained after removing the internal geomagnetic field and quiet time contributions can be considered as a proxy for storm time currents and are found to follow the temporal profile of Dst index very closely. These variations at the equatorial crossings recorded by multiple-spacecraft are used to estimate the Dst values and are found to have a good match with the ground-based Dst index. The average deviation between these two is around 4–13%. We have estimated the asymmetry by taking the difference between the magnetic field variations at two local time sectors separated by 12 hr. The estimated asymmetry shows a good match with the AsyH-index, especially when satellite traverses in the dawn-dusk sector. In general, the magnetic field variations are stronger in the night-to-dusk sector than day-to-dawn sector, which could be due to the larger pressure-gradients near night-to-dusk caused by ion movements. The important advantage of Swarm mission is that it provides an opportunity to investigate the longitudinal gradients in the storm time magnetic fields. It is observed that in general, the gradients are stronger during the main phase of the storm, centered near the equator with a latitudinal width of ~20–30° in both the hemispheres, and are supportive to the scenario of particle-injection from the magnetotail. The stronger gradients are observed at higher latitudes (~40°) during the episodes of substorms and might be associated with the ionospheric/field-aligned currents.

DOI： 10.1029/2018JA025692

Transient ionization of the mesosphere during auroral breakup: Arase satellite and ground-based conjugate observations at Syowa Station Reviewed Open Access

Ryuho Kataoka, Takanori Nishiyama, Yoshimasa Tanaka, Akira Kadokura, Herbert Akihito Uchida, Yusuke Ebihara, Mitsumu K. Ejiri, Yoshihiro Tomikawa, Masaki Tsutsumi, Kaoru Sato, Yoshizumi Miyoshi, Kazuo Shiokawa, Satoshi Kurita, Yoshiya Kasahara, Mitsunori Ozaki, Keisuke Hosokawa, Shoya Matsuda, Iku Shinohara, Takeshi Takashima, Tatsuhiko Sato, Takefumi Mitani, Tomoaki Hori, Nana Higashio

EARTH PLANETS AND SPACE Vol. 71 ( 1 ) page： 9 2019.1

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGEROPEN

Transient mesospheric echo in the VHF range was detected at an altitude of 65-70km during the auroral breakup that occurred from 2220 to 2226 UT on June 30, 2017. During this event, the footprint of the Arase satellite was located within the field of view of the all-sky imagers at Syowa Station in the Antarctic. Auroral observations at Syowa Station revealed the dominant precipitation of relatively soft electrons during the auroral breakup. A corresponding spike in cosmic noise absorption was also observed at Syowa Station, while the Arase satellite observed a flux enhancement of >100keV electrons and a broadband noise without detecting chorus waves or electromagnetic ion cyclotron waves. A general-purpose Monte Carlo particle transport simulation code was used to quantitatively evaluate the ionization in the middle atmosphere. Results of this study indicate that the precipitation of energetic electrons of >100keV, rather than X-rays from the auroral electrons, played a dominant role in the transient and deep (65-70km) mesospheric ionization during the observed auroral breakup.

DOI： 10.1186/s40623-019-0989-7

Visualization of rapid electron precipitation via chorus element wave-particle interactions Reviewed Open Access

Mitsunori Ozaki, Yoshizumi Miyoshi, Kazuo Shiokawa, Keisuke Hosokawa, Shin-ichiro Oyama, Ryuho Kataoka, Yusuke Ebihara, Yasunobu Ogawa, Yoshiya Kasahara, Satoshi Yagitani, Yasumasa Kasaba, Atsushi Kumamoto, Fuminori Tsuchiya, Shoya Matsuda, Yuto Katoh, Mitsuru Hikishima, Satoshi Kurita, Yuichi Otsuka, Robert C. Moore, Yoshimasa Tanaka, Masahito Nose, Tsutomu Nagatsuma, Nozomu Nishitani, Akira Kadokura, Martin Connors, Takumi Inoue, Ayako Matsuoka, Iku Shinohara

NATURE COMMUNICATIONS Vol. 10 ( 1 ) page： 257 2019.1

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

Chorus waves, among the most intense electromagnetic emissions in the Earth's magnetosphere, magnetized planets, and laboratory plasmas, play an important role in the acceleration and loss of energetic electrons in the plasma universe through resonant interactions with electrons. However, the spatial evolution of the electron resonant interactions with electromagnetic waves remains poorly understood owing to imaging difficulties. Here we provide a compelling visualization of chorus element wave-particle interactions in the Earth's magnetosphere. Through in-situ measurements of chorus waveforms with the Arase satellite and transient auroral flashes from electron precipitation events as detected by 100-Hz video sampling from the ground, Earth's aurora becomes a display for the resonant interactions. Our observations capture an asymmetric spatial development, correlated strongly with the amplitude variation of discrete chorus elements. This finding is not theoretically predicted but helps in understanding the rapid scattering processes of energetic electrons near the Earth and other magnetized planets.

DOI： 10.1038/s41467-018-07996-z

PRELIMINARY RESULTS OF SIMULTANEOUS RECORDING OF AURORAL AND GEOMAGNETIC PULSATIONS AT THE ISTP SB RAS STATION ISTOK Reviewed Open Access

Beletskii A. B., Rakhmatulin R. A., Syrenova T. Ye, Vasilev R. V., Mikhalev A. V, Pashinin A. Yu, Shiokawa K., Nishitani N.

SOLAR-TERRESTRIAL PHYSICS Vol. 5 ( 2 ) page： 39 - 44 2019

Preliminary results of simultaneous recording of auroral and geomagnetic pulsations at the ISTP SB RAS station Istok Reviewed Open Access

Beletskii A.B., Rakhmatulin R.A., Syrenova T.Y., Vasilev R.V., Mikhalev A.V., Pashinin A.Y., Shiokawa K., Nishitani N.

Solnecno Zemnaa Fizika Vol. 5 ( 2 ) page： 43 - 48 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：Solnecno Zemnaa Fizika

The paper presents the results on first synchronous observations of variations in auroral luminosity and geomagnetic field, made with high temporal resolution at the ISTP SB RAS high-latitude station Istok (70° N, 88° E) in September–December 2018. Auroras were recorded with all-sky camera, pulsations in the auroras were recorded by a photometer in four spectral ranges with silicon photomultipliers. Continuous monitoring of geomagnetic pulsations was performed using a LEMI-30 three-component induction magnetometer. Both synchronous bursts of auroras and magnetic field pulsations, as well as disturbances of auroras, not accompanied by disturbances in the geomagnetic field, were observed. We note that the photometer clearly recorded short-period (~20 min) variations in in auroral luminosity. At the same time, some instability of the photometer signal level occurred at sufficiently long time intervals. In the photometer data, there are powerful signal bursts, probably of a hardware nature. Nevertheless, the temporary distribution analysis of the registration moments (registration frequency) of signal bursts indicates the possible dependence of the burst registration frequency on the geomagnetic activity level.

DOI： 10.12737/szf-52201906

Spatiotemporal development of pulsating auroral patch associated with discrete chorus elements: Arase and PWING observations Reviewed

Ozaki M., Shiokawa K., Miyoshi Y., Hosokawa K., Oyama S., Yagitani S., Kasahara Y., Kasaba Y., Matsuda S., Kataoka R., Ebihara Y., Ogawa Y., Otsuka Y., Kurita S., Moore R. C., Tanaka Y. -M., Nose M., Nagatsuma T., Connors M., Nishitani N., Hikishima M., Kumamoto A., Tsuchiya F., Kadokura A., Nishiyama T., Inoue T., Imamura K., Matsuoka A., Shinohara I.

2019 URSI ASIA-PACIFIC RADIO SCIENCE CONFERENCE (AP-RASC) 2019

Temporal and Spatial Correspondence of Pc1/EMIC Waves and Relativistic Electron Precipitations Observed with Ground-Based Multi-Instruments on 27 March 2017 Reviewed Open Access

Hirai, A, F. Tsuchiya, T. Obara, Y. Kasaba, Y. Katoh, H. Misawa, K. Shiokawa, Y. Miyoshi, S. Kurita, S. Matsuda, M. Connors, T. Nagatsuma, K. Sakaguchi, Y. Kasahara, A. Kumamoto, A. Matsuoka, M. Shoji, I. Shinohara, J. M. Albert

Geophysical Research Letters Vol. 45 ( 24 ) page： 13182 - 13191 2018.12

Electrostatic Electron Cyclotron Harmonic Waves as a Candidate to Cause Pulsating Auroras Reviewed Open Access

M. Fukizawa, T. Sakanoi, Y. Miyoshi, K. Hosokawa, K. Shiokawa, Y. Katoh, Y. Kazama, A. Kumamoto, F. Tsuchiya, Y. Miyashita, Y. M. Tanaka, Y. Kasahara, M. Ozaki, A. Matsuoka, S. Matsuda, M. Hikishima, S. Oyama, Y. Ogawa, S. Kurita, R. Fujii

Geophysical Research Letters Vol. 45 ( 23 ) page： 12661 - 12668 2018.12

Language：English Publishing type：Research paper (scientific journal)

©2018. American Geophysical Union. All Rights Reserved. Pulsating auroras (PsAs) are thought to be generated by precipitating electrons scattered by lower-band chorus (LBC) waves near the magnetic equator. One-to-one correlation between the LBC intensity and the PsA intensity has been reported. Electrostatic electron cyclotron harmonic (ECH) waves can also scatter electrons. However, direct correlation between ECH and PsA has not been reported yet. In this study, using a coordinated Exploration of energization and Radiation in Geospace (Arase) satellite and ground-based imager observation, we report that not only LBC but also ECH have correlation with PsA. We estimated the precipitating electron energy by assuming that the time lag when the cross-correlation coefficient became the highest was travel time of electrons from the modulation region. We found that the estimated energies show reasonable values as the cyclotron resonance energy of each wave.

DOI： 10.1029/2018GL080145

Rapid Loss of Relativistic Electrons by EMIC Waves in the Outer Radiation Belt Observed by Arase, Van Allen Probes, and the PWING Ground Stations Open Access

Kurita S, Miyoshi Y, Shiokawa K, Higashio N, Mitani T, Takashima T, Matsuoka A, Shinohara I, Kletzing C. A, Blake J. B, Claudepierre S. G, Connors M, Oyama S, Nagatsuma T, Sakaguchi K, Baishev D, Otsuka Y

GEOPHYSICAL RESEARCH LETTERS Vol. 45 ( 23 ) page： 12720 - 12729 2018.12

Large-Scale Ducting of Pc1 Pulsations Observed by Swarm Satellites and Multiple Ground Networks Reviewed Open Access

Hyangpyo Kim, Junga Hwang, Jaeheung Park, Yukinaga Miyashita, Kazuo Shiokawa, Ian R. Mann, Tero Raita, Jaejin Lee

GEOPHYSICAL RESEARCH LETTERS Vol. 45 ( 23 ) page： 12703 - 12712 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Low Earth orbit satellites frequently encounter Pc1 pulsations, but most have been observed with limited latitudinal extent or short lifetime. In this study we analyze two large-scale Pc1 pulsations (both latitudinally wide and long-lasting) generated by ionospheric ducting effect using Swarm and ground magnetometers on 25 June and 3 September 2015. Swarm observed the 25 June pulsations on both dayside and nightside during the storm time substorm (a strong geomagnetic storm on 23 June with D-st = - 204 nT). We found the Pc1 pulsations were pervasive in both magnetic local time sectors of dayside and nightside for at least 2 hr. Another large Pc1 pulsation on 3 September was observed during a nonstorm substorm period. We conclude that (1) ionospheric ducting can transmit Pc1 waves to a wide range of L shells, (2) geomagnetic storm is not a prerequisite for such large-scale ducting, and (3) wave intensity can abruptly decrease across sharp gradients in the ionospheric plasma density.

DOI： 10.1029/2018GL080693

Energetic electron precipitation associated with pulsating aurora observed by VLF radio propagation during recovery phase of substorm on 27 March 2017 Reviewed Open Access

Tsuchiya,F, A. Hirai, T. Obara, H. Misawa, S. Kurita, Y. Miyoshi, K. Shiokawa, M. Connors, M. Ozaki, Y. Kasahara, A. Kumamoto, Y. Kasaba, A. Matsuoka, M. Shoji, I. Shinohara

Geophysical Research Letters Vol. 45 ( 23 ) page： 12651 - 12660 2018.12

The ARASE (ERG) magnetic field investigation Reviewed Open Access

Matsuoka A, Teramoto M, Nomura R, Nosé M, Fujimoto A, Tanaka Y, Shinohara M, Nagatsuma T, Shiokawa K, Obana Y, Miyoshi Y, Mita M, Takashima T, Shinohara I

Earth, Planets and Space Vol. 70 ( 1 ) 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER HEIDELBERG

© 2018, The Author(s). The fluxgate magnetometer for the Arase (ERG) spacecraft mission was built to investigate particle acceleration processes in the inner magnetosphere. Precise measurements of the field intensity and direction are essential in studying the motion of particles, the properties of waves interacting with the particles, and magnetic field variations induced by electric currents. By observing temporal field variations, we will more deeply understand magnetohydrodynamic and electromagnetic ion-cyclotron waves in the ultra-low-frequency range, which can cause production and loss of relativistic electrons and ring-current particles. The hardware and software designs of the Magnetic Field Experiment (MGF) were optimized to meet the requirements for studying these phenomena. The MGF makes measurements at a sampling rate of 256 vectors/s, and the data are averaged onboard to fit the telemetry budget. The magnetometer switches the dynamic range between ± 8000 and ± 60,000 nT, depending on the local magnetic field intensity. The experiment is calibrated by preflight tests and through analysis of in-orbit data. MGF data are edited into files with a common data file form

DOI： 10.1186/s40623-018-0800-1

Comparison of gravity wave propagation directions observed by mesospheric airglow imaging at three different latitudes using the M-transform Reviewed Open Access

Septi Perwitasari, Takuji Nakamura, Masaru Kogure, Yoshihiro Tomikawa, Mitsumu K. Ejiri, Kazuo Shiokawa

ANNALES GEOPHYSICAE Vol. 36 ( 6 ) page： 1597 - 1605 2018.11

Language：English Publishing type：Research paper (scientific journal) Publisher：COPERNICUS GESELLSCHAFT MBH

We developed user-friendly software based on Matsuda et al.'s (2014) 3D-FFT method (Matsuda-transform, M-transform) for airglow imaging data analysis as a function of Interactive Data Language (IDL). Users can customize the range of wave parameters to process when executing the program. The input for this function is a 3-D array of a time series of a 2-D airglow image in geographical coordinates. We applied this new function to mesospheric airglow imaging data with slightly different observation parameters obtained for the period of April-May at three different latitudes: Syowa Station, the Antarctic (69 degrees S, 40 degrees E); Shigaraki, Japan (35 degrees N, 136 degrees E); and Tomohon, Indonesia (1 degrees N, 122 degrees E). The day-to-day variation of the phase velocity spectrum at the Syowa Station is smaller and the propagation direction is mainly westward. In Shigaraki, the day-to-day variation of the horizontal propagation direction is larger than that at the Syowa Station; the variation in Tomohon is even larger. In Tomohon, the variation of the nightly power spectrum magnitude is remarkable, which indicates the intermittency of atmospheric gravity waves (AGWs). The average nightly spectrum obtained from April-May shows that the dominant propagation is westward with a phase speed < 50 m s(-1) at the Syowa Station and east-southeastward with a phase speed of up to similar to 80 m s(-1) in Shigaraki. The day-to-day variation in Tomohon is too strong to discuss average characteristics; however, a phase speed of up to similar to 100 m s(-1) and faster is observed. The corresponding background wind profiles derived from MERRA-2 indicate that wind filtering plays a significant role in filtering out waves that propagate eastward at the Syowa Station. On the other hand, the background wind is not strong enough to filter out relatively high-speed AGWs in Shigaraki and Tomohon and the dominant propagation direction is likely related to the distribution and characteristics of the source region, at least in April and May.

DOI： 10.5194/angeo-36-1597-2018

Microscopic Observations of Pulsating Aurora Associated With Chorus Element Structures: Coordinated Arase Satellite-PWING Observations Reviewed Open Access

Ozaki M, Shiokawa K, Miyoshi Y, Hosokawa K, Oyama S, Yagitani S, Kasahara Y, Kasaba Y, Matsuda S, Kataoka R, Ebihara Y, Ogawa Y, Otsuka Y, Kurita S, Moore R. C, Tanaka Y. -M, Nose M, Nagatsuma T, Connors M, Nishitani N, Katoh Y, Hikishima M, Kumamoto A, Tsuchiya F, Kadokura A, Nishiyama T, Inoue T, Imamura K, Matsuoka A, Shinohara I

GEOPHYSICAL RESEARCH LETTERS Vol. 45 ( 22 ) page： 12125 - 12134 2018.11

Language：English Publishing type：Research paper (scientific journal)

Rapid (<1 s) intensity modulation of pulsating auroras is caused by successive chorus elements as a response to wave-particle interactions in the magnetosphere. Here we found that a pulsating auroral patch responds to the time spacing for successive chorus elements and possibly to chorus subpacket structures with a time scale of tens of milliseconds. These responses were identified from coordinated Arase satellite and ground (Gakona, Alaska) observations with a high-speed auroral imager (100 Hz). The temporal variations of auroral intensity in a few-hertz frequency range exhibited a spatial concentration at the lower-latitude edge of the auroral patch. The spatial evolution of the auroral patch showed repeated expansion/contraction with tens of kilometer scales in the ionosphere, which could be spatial behaviors in the wave-particle interactions. These observations indicate that chorus elements evolve coherently within the auroral patch, which is approximately 900 km in the radial and longitudinal directions at the magnetic equator.

DOI： 10.1029/2018GL079812

Statistical Analysis of SAR Arc Detachment From the Main Oval Based on 11-Year, AII-sky Imaging Observation at Athabasca, Canada Reviewed Open Access

Yuki Takagi, Kazuo Shiokawa, Yuichi Otsuka, Martin Connors, Ian Schofield

GEOPHYSICAL RESEARCH LETTERS Vol. 45 ( 21 ) page： 11539 - 11546 2018.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report the first statistical analysis of stable auroral red (SAR) arc detachments from the main auroral oval, using 630-nm all-sky cooled-Charge Coupled Device images obtained at Athabasca (magnetic latitude = 61.7 degrees N), Canada. SAR arc detachments from the main oval can be an important way of monitoring the characteristics of ring current particle injection in the inner magnetosphere. We analyzed all-sky images obtained for 11 years from 2006 to 2016 and found 163 SAR arc detachment events. The SAR arc detachments tend to occur in the premidnight sector, indicating the ring current ion drift to the dusk sector. The SAR arc detachments also tend to occur at the beginning of the substorm recovery phase, suggesting that the SAR arcs detach from the main oval as the main auroral oval returns to higher latitudes. The equatorward velocities of detached SAR arcs are from -100 m/s (poleward) to +200 m/s (equatorward), corresponding to magnetospheric electric fields from -1 to +2 mV/m.Plain Language, Summary Stable auroral red (SAR) arcs are the optical emissions caused by low-energy electron precipitation into the ionosphere from the inner magnetosphere close to the earth. In this paper, we report the first statistical analysis of SAR arc detachments from the main auroral oval, using all-sky cooled-Charge Coupled Device images measured at a wavelength of 630.0 nm obtained at Athabasca, Canada, which is located at latitudes just lower than the auroral zone latitudes. SAR arc detachments from the main oval can be an important way of monitoring the characteristics of high-energy particle injection in the inner magnetosphere. We analyzed 11-year all-sky images from 2006 to 2016 and found 163 SAR arc detachment events. The SAR arc detachments tend to occur premidnight, indicating the high-energy ion drift to the dusk sector. We also found that the SAR arc detachments tend to occur at the beginning of the substorm recovery phase. This likely indicates that the SAR arcs detach from the high-latitude aurora as the main aurora returns to higher latitudes at the beginning of the recovery phase. The equatorward velocities of detached SAR arcs are also estimated from the analysis.

DOI： 10.1029/2018GL079615

Variability of the Sun and Its Terrestrial Impacts Reviewed

Katya Georgieva, Kazuo Shiokawa

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 180 page： 1 - 2 2018.11

Statistical Study of Phase Relationship Between Magnetic and Plasma Pressures in the Near-Earth Nightside Magnetosphere Using the THEMIS-E Satellite Reviewed Open Access

Katsuki Nishi, Kazuo Shiokawa, Karl-Heinz Glassmeier, Johannes Z. D. Mieth

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 123 ( 11 ) page： 9517 - 9531 2018.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Distributions of plasma and magnetic pressures are the basic information to investigate macroscopic dynamics of the Earth's magnetosphere. Several studies have been made on magnetic and plasma pressures and macroscopic plasma instabilities in the magnetosphere. However, correlation between magnetic and plasma pressure variations has not been statistically investigated. In this paper, we analyze the statistical characteristics of the phase relationships between variations of magnetic and plasma pressures at frequencies of 4-15 mHz using 2 years of the THEMIS-E satellite data in the nightside magnetosphere. Spectral peaks with coherence greater than 0.85 between magnetic and plasma pressures for 1-hr time segments were selected. The average occurrence rates of the phase relationships are antiphase (within +/- 10 degrees from 180 degrees), 39.75%; in-phase (within +/- 10 degrees from 0 degrees), 0.73%; and other phases (10-170 degrees), 49.83%. For the other-phase events, the phase differences are much closer to antiphase rather than to in-phase. Thus, we conclude that the two pressure variations tend to be antiphase. The antiphase and in-phase relationships are observed mainly at radial distances outside 8 R-E and inside 8 R-E, respectively. The high occurrence region of antiphase relationship is in the dawnside during magnetically quiet times and shifts to dusk side at active times defined as Dst < -10 nT. The occurrence rates of the phase relationships do not change significantly depending on the AE and Dst indices, plasma beta, and IMF-B-z. Based on these results, we discuss the correspondence between the phase relationships and the possible magnetohydrodynamic force balances that can produce these phase relationships.

DOI： 10.1029/2018JA025846

サブオーロラ帯におけるEMIC波動と高エネルギー電子降下観測 Open Access

平井あすか, 土屋史紀, 小原隆博, 笠羽康正, 加藤雄人, 三澤浩昭, 塩川和夫, 三好由純, 栗田怜, Martin Connors

宇宙航空研究開発機構特別資料: 第15回「宇宙環境シンポジウム」講演論文集 page： 11 - 16 2018.11

Language：Japanese Publishing type：Research paper (scientific journal)

放射線帯外帯の相対論的電子は、磁気圏内で発生するプラズマ波動との相互作用により散乱され地球大気に降下する。この過程は、磁気嵐の主相における外帯消失の要因の一つと考えられており、降下した相対論的電子は、国際宇宙ステーションや低軌道衛星への悪影響、下部電離圏での電子密度増加に伴う通信障害を引き起こし得る。本研究では、放射線帯の相対論的電子を降下消失させる電磁イオンサイクロトロン（EMIC）波動に着目した。電子降下は、VLF/LF帯の人工電波を用いて観測した。地上と電離圏下端の間を長距離伝搬する電波の信号は、電子降下に伴う電離圏D領域高度での局所的な擾乱により振幅・位相変調をうける。本研究では、複合地上観測により、2017年3月27日の磁気嵐主相時のEMIC波動とそれに伴う相対論的電子降下の時空間対応を調べた。その結果、数10秒から数分の時間スケールで変化するEMIC波動強度の増大時に、相対論的電子が散乱され大気に降下消失することが明らかとなった。

Purple Auroral Rays and Global Pc1 Pulsations Observed at the CIR-Associated Solar Wind Density Enhancement on 21 March 2017 Reviewed Open Access

K. Shiokawa, M. Ozaki, A. Kadokura, Y. Endo, T. Sakanoi, S. Kurita, Y. Miyoshi, S. I. Oyama, M. Connors, I. Schofield, J. M. Ruohoniemi, M. Nośe, T. Nagatsuma, K. Sakaguchi, D. G. Baishev, A. Pashinin, R. Rakhmatulin, B. Shevtsov, I. Poddelsky, M. Engebretson, Tero Raita, Y. M. Tanaka, M. Shinohara, M. Teramoto, R. Nomura, A. Fujimoto, A. Matsuoka, N. Higashio, T. Takashima, I. Shinohara, Jay M. Albert

Geophysical Research Letters Vol. 45 ( 20 ) page： 10819 - 10828 2018.10

Language：English Publishing type：Research paper (scientific journal)

©2018. American Geophysical Union. All Rights Reserved. This paper reports two unique auroral features: postmidnight purple auroral rays and global Pc1 geomagnetic pulsations, observed before the onset of the corotating interaction region (CIR) storm of 21 March 2017, at the beginning of the first campaign of the new Particles and Waves in the Inner magnetosphere using Ground-based network observation (PWING) longitudinal ground network with the Arase satellite. The purple auroral rays were observed from ~0315 to 0430 UT (~03–04 magnetic local time) in the northeastern sky at Husafell, Iceland (magnetic latitude: 64.9°N). We newly propose that the entry of high-density CIR plasma into the magnetotail created purple auroral rays in the sunlit ionosphere. Pc1 geomagnetic pulsations at frequencies of 0–0.5 Hz were observed after ~00 UT over a wide local time range, of 13 hr, from midnight to afternoon sectors at subauroral latitudes associated with CIR arrival. These results indicate preconditioning of the magnetosphere due to crossing of a CIR.

DOI： 10.1029/2018GL079103

Global Distribution of ULF Waves During Magnetic Storms: Comparison of Arase, Ground Observations, and BATSRUSC plus CRCM Simulation Reviewed Open Access

Naoko Takahashi, Kanako Seki, Mariko Teramoto, Mei-Ching Fok, Yihua Zheng, Ayako Matsuoka, Nana Higashio, Kazuo Shiokawa, Dmitry Baishev, Akimasa Yoshikawa, Tsutomu Nagatsuma

GEOPHYSICAL RESEARCH LETTERS Vol. 45 ( 18 ) page： 9390 - 9397 2018.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

During 26-29 March 2017 magnetic storm, the Arase satellite observed typical ultra low frequency (ULF) waves and acceleration of relativistic electrons. We simulate the global distribution of these ULF waves using CRCM with BATSRUS global magnetospheric magnetohydrodynamic model. The simulation can qualitatively reproduce the ULF waves observed by Arase at frequencies of 2-3 mHz. However, the simulated ULF wave power is 1-2 orders of magnitude smaller than the observation. The simulated ULF wave activity has a good correlation with the solar-wind dynamic pressure variation, while the wave activity on the ground is enhanced even during the recovery phase, possibly due to the Kelvin-Helmholtz instability and/or substorms. We also study the 3-6 April 2017 magnetic storm, in which low ULF wave activity and weak acceleration of relativistic electrons are seen. We suggest that the existence of ULF waves plays an important role in accelerating electrons up to relativistic energies.Plain Language Summary The Earth has the region of space that is controlled by the Earth's magnetic field, called the magnetosphere. When the temporary disturbance of the magnetosphere (magnetic storm) occurs, extremely high-energy electrons (a few MeV) accelerate around the Earth. It is considered that periodic waves with a frequency of 1-20 mHz, known as ultra low frequency (ULF) waves, play an important role in accelerating electrons up to relativistic energies. On 27 March 2017, Japanese satellite, called as "Arase," successfully observed ULF waves. We focus on this ULF waves and investigate the global activity of ULF waves using both numerical simulations and observations. The numerical simulation using in this study qualitatively reproduced the enhancement of ULF waves with a frequency range of 1.6-6.7 mHz, but its intensity is smaller than the Arase satellite observation. Comparing to ground observations, we found that the global ULF wave activity estimated by the numerical simulation is strongly affected by the dynamic pressure enhancement caused by a stream of charged particles from the Sun. In addition, we suggest that the ULF wave activity might affect the acceleration characteristics of high-energy electrons around the Earth.

DOI： 10.1029/2018GL078857

Investigation of Nighttime MSTIDS Observed by Optical Thermosphere Imagers at Low Latitudes: Morphology, Propagation Direction, and Wind Filtering Reviewed Open Access

Figueiredo C, A. O. B, Takahashi H, Wrasse C. M, Otsuka Y, Shiokawa K, Barros D

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 123 ( 9 ) page： 7843 - 7857 2018.9

Magnetospheric Source Region of Auroral Finger-like Structures Observed by the RBSP-A Satellite Reviewed Open Access

Katsuki Nishi, Kazuo Shiokawa, Harlan Spence

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 123 ( 9 ) page： 7513 - 7522 2018.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Auroral finger-like structures appear equatorward of the auroral oval in the diffuse auroral region and contribute to the auroral fragmentation into patches. A previous report of the first conjugate observation of auroral finger-like structures using a Time History of Events and Macroscale Interactions during Substorms (THEMIS) Ground-Based Observatories camera and the THEMIS-E satellite at a radial distance of similar to 8 R-E showed antiphase oscillations of magnetic and plasma pressures in the dawnside plasma sheet. In the present study, we report another simultaneous observation of auroral finger-like structures at Gillam, Canada, at similar to 0900UT (0230 magnetic local time) on 14 November 2014 with the Radiation Belt Storm Probes satellites at 5.8R(E) in the inner magnetosphere. From this simultaneous observation event, we obtained the following observations. (1) Auroral finger-like structures developed poleward in the equatorward moving auroral arc at the equatorward edge of the auroral oval. (2) Both the electron and ion OMNI fluxes measured by HOPE increased at approximate to 0900UT as the satellite footprint entered the auroral region, indicating that the satellite was crossing the observed auroral finger-like structures. (3) The absolute value of magnetic pressure was several times that of the plasma pressure, and no systematic phase relationship was identified between the magnetic and plasma pressures, unlike that in the THEMIS case. Based on these observations, we discuss two possible causes of the observed finger-like structures, namely, pressure-driven instability in the magnetosphere and gradient drift instability in the ionosphere. In this paper, the latter possibility is newly suggested to develop in the equatorward moving aurora associated with the westward electric field in the equatorward ionospheric density gradient.Plain Language Summary We report the conjugate observation of auroral finger-like structures using ground-based all-sky imager and the RBSP-A satellite. Such a report of conjugate observation of auroral finger-like structures with the RBSP-A satellite in the inner magnetosphere is for the first time. The auroral finger-like structures can be a cause of the auroral fragmentation into patches. From the present observation, we suggest that the gradient drift instability in the ionospheric plasma can be a cause of the auroral finger-like structures.

DOI： 10.1029/2018JA025480

Comparison of gravity wave propagation direction observed by mesospheric airglow imaging at three different latitudes by using M-transform Reviewed

Septi Perwitasari, Takuji Nakamura, Masaru Kogure, Yoshihiro Tomikawa, Mitsumu K. Ejiri, Kazuo Shiokawa

Annales Geophysicae Discussions page： 1 - 15 2018.9

Statistical Analysis of the Phase Velocity Distribution of Mesospheric and Ionospheric Waves Observed in Airglow Images Over a 16-Year Period: Comparison Between Rikubetsu and Shigaraki, Japan Reviewed Open Access

Tsuchiya Satoshi, Shiokawa Kazuo, Fujinami Hatsuki, Otsuka Yuichi, Nakamura Takuji, Yamamoto Mamoru

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 123 ( 8 ) page： 6930-6947 2018.8

EMIC Wave Events During the Four GEM QARBM Challenge Intervals Reviewed Open Access

Engebretson M. J, Posch J. L, Braun D. J, Li W, Ma Q, Kellerman A. C, Huang C. -L, Kanekal S. G, Kletzing C. A, Wygant J. R, Spence H. E, Baker D. N, Fennell J. F, Angelopoulos V, Singer H. J, Lessard M. R, Horne R. B, Raita T, Shiokawa K, Rakhmatulin R, Dmitriev E, Ermakova E

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 123 ( 8 ) page： 6394 - 6423 2018.8

On the Role of Thermospheric Winds and Sporadic E Layers in the Formation and Evolution of Electrified MSTIDs in Geomagnetic Conjugate Regions Reviewed Open Access

Narayanan V. L, Shiokawa K, Otsuka Y, Neudegg D

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 123 ( 8 ) page： 6957 - 6980 2018.8

Geospace exploration project ERG Reviewed Open Access

Yoshizumi Miyoshi, Iku Shinohara, Takeshi Takashima, Kazushi Asamura, Nana Higashio, Takefumi Mitani, Satoshi Kasahara, Shoichiro Yokota, Yoichi Kazama, Shiang-Yu Wang, Sunny W. Y. Tam, Paul T. P. Ho, Yoshiya Kasahara, Yasumasa Kasaba, Satoshi Yagitani, Ayako Matsuoka, Hirotsugu Kojima, Yuto Katoh, Kazuo Shiokawa, Kanako Seki

EARTH PLANETS AND SPACE Vol. 70 ( 1 ) 2018.6

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

The Exploration of energization and Radiation in Geospace (ERG) project explores the acceleration, transport, and loss of relativistic electrons in the radiation belts and the dynamics for geospace storms. This project consists of three research teams for satellite observation, ground-based network observation, and integrated data analysis/simulation. This synergetic approach is essential for obtaining a comprehensive understanding of the relativistic electron generation/loss processes of the radiation belts as well as geospace storms through cross-energy/cross-regional couplings, in which different plasma/particle populations and regions are strongly coupled with each other. This paper gives an overview of the ERG project and presents the initial results from the ERG (Arase) satellite.

DOI： 10.1186/s40623-018-0862-0

Equatorial plasma bubble seeding by MSTIDs in the ionosphere Reviewed Open Access

Takahashi Hisao, Wrasse Cristiano Max, Oliveira Barros Figueiredo Cosme Alexandre, Barros Diego, Abdu Mangalathayil Ali, Otsuka Yuichi, Shiokawa Kazuo

PROGRESS IN EARTH AND PLANETARY SCIENCE Vol. 5 2018.6

Periodic Oscillations in the D Region Ionosphere After the 2011 Tohoku Earthquake Using LF Standard Radio Waves Reviewed Open Access

Hiroyo Ohya, Fuminori Tsuchiya, Yuta Takishita, Hiroyuki Shinagawa, Kenro Nozaki, Kazuo Shiokawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 123 ( 6 ) page： 5261 - 5270 2018.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report the first observations of similar to 100-s periodic oscillations of intensity in low-frequency (LF) standard radio waves over Japan at 05:51-05:56 UT, which was about 4min and 42s after mainshock onset of the 2011 off the Pacific coast of Tohoku earthquake on 11 March 2011 (Mw 9.0). The LF radio wave propagation paths used in this study were JJY (Japan, 60kHz)-Rikubetsu (RKB, Japan), and BPC (China, 68.5 kHz)-RKB, where the minimum distances between the epicenter and the LF propagation paths were 413.6 and 561.5 km, respectively. The observed modulations in intensity and phase were about 0.1 dB and 0.5 degrees, respectively. Based on a numerical simulation of the neutral atmosphere and the wave-hop method, the occurrence time of the similar to 100-s periodic oscillations was in good agreement with the total propagation time of the Rayleigh wave that spread concentrically from the epicenter to the LF propagation paths and acoustic waves propagating vertically from the Earth's surface to the bottom of the ionosphere. Variations in synthesized electric field intensity of ground waves and sky waves, calculated by the wave hop method up to 10 hops, reproduced similar similar to 100-s periodic oscillations that were caused by the difference in arrival time of the acoustic waves excited by the Rayleigh waves at each hop point. The amplitude of the D region electron density variations at 70km altitude during the similar to 100-s periodic oscillation was estimated to be about 1% compared to the background electron density, based on the numerical simulation.

DOI： 10.1029/2018JA025289

Medium-Scale Traveling Ionospheric Disturbances Observed by Detrended Total Electron Content Maps Over Brazil Reviewed Open Access

Figueiredo C. A. O. B., Takahashi H., Wrasse C. M., Otsuka Y., Shiokawa K., Barros D.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 123 ( 3 ) page： 2215-2227 2018.3

Discovery of 1Hz Range Modulation of Isolated Proton Aurora at Subauroral Latitudes Open Access

Ozaki M., Shiokawa K., Miyoshi Y., Kataoka R., Connors M., Inoue T., Yagitani S., Ebihara Y., Jun C. -W., Nomura R., Sakaguchi K., Otsuka Y., Uchida H. A., Schofield I., Danskin D. W.

GEOPHYSICAL RESEARCH LETTERS Vol. 45 ( 3 ) page： 1209-1217 2018.2

Observations of aurora and electromagnetic disturbances originated from dynamic plasma variations in the Earth's inner magnetosphere Reviewed Open Access

Shiokawa Kazuo

Meeting Abstracts of the Physical Society of Japan Vol. 73.1 ( 0 ) page： 766 - 766 2018

First Study on the Occurrence Frequency of Equatorial Plasma Bubbles over West Africa Using an All-Sky Airglow Imager and GNSS Receivers Open Access

Okoh Daniel, Rabiu Babatunde, Shiokawa Kazuo, Otsuka Yuichi, Segun Bolaji, Falayi Elijah, Onwuneme Sylvester, Kaka Rafiat

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 122 ( 12 ) page： 12430-12444 2017.12

Ground-based instruments of the PWING project to investigate dynamics of the inner magnetosphere at subauroral latitudes as a part of the ERG-ground coordinated observation network Open Access

Shiokawa Kazuo, Katoh Yasuo, Hamaguchi Yoshiyuki, Yamamoto Yuka, Adachi Takumi, Ozaki Mitsunori, Oyama Shin-Ichiro, Nose Masahito, Nagatsuma Tsutomu, Tanaka Yoshimasa, Otsuka Yuichi, Miyoshi Yoshizumi, Kataoka Ryuho, Takagi Yuki, Takeshita Yuhei, Shinbori Atsuki, Kurita Satoshi, Hori Tomoaki, Nishitani Nozomu, Shinohara Iku, Tsuchiya Fuminori, Obana Yuki, Suzuki Shin, Takahashi Naoko, Seki Kanako, Kadokura Akira, Hosokawa Keisuke, Ogawa Yasunobu, Connors Martin, Ruohoniemi J. Michael, Engebretson Mark, Turunen Esa, Ulich Thomas, Manninen Jyrki, Raita Tero, Kero Antti, Oksanen Arto, Back Marko, Kauristie Kirsti, Mattanen Jyrki, Baishev Dmitry, Kurkin Vladimir, Oinats Alexey, Pashinin Alexander, Vasilyev Roman, Rakhmatulin Ravil, Bristow William, Karjala Marty

EARTH PLANETS AND SPACE Vol. 69 2017.11

Special Issue "Global data systems for the study of solar-terrestrial variability"

Watanabe Takashi, Iyemori Toshihiko, Shiokawa Kazuo, Zhang Jie, Kanekal Shrikanth G., Nishitani Nozomu

EARTH PLANETS AND SPACE Vol. 69 2017.11

Geomagnetically conjugate observations of ionospheric and thermospheric variations accompanied by a midnight brightness wave at low latitudes (vol 69, 112, 2017) Reviewed Open Access

D. Fukushima, K. Shiokawa, Y. Otsuka, M. Kubota, T. Yokoyama, M. Nishioka, S. Komonjinda, C. Y. Yatini

EARTH PLANETS AND SPACE Vol. 69 2017.11

GPS amplitude and phase scintillation associated with polar cap auroral forms

Jayachandran P. T., Hamza A. M., Hosokawa K., Mezaoui H., Shiokawa K.

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 164 page： 185-191 2017.11

Statistical analysis of severe magnetic fluctuations in the near-Earth plasma sheet observed by THEMIS-E Open Access

Xu Heqiucen, Shiokawa Kazuo, Fruehauff Dennis

ANNALES GEOPHYSICAE Vol. 35 ( 5 ) page： 1131-1142 2017.10

Geomagnetically conjugate observations of ionospheric and thermospheric variations accompanied by a midnight brightness wave at low latitudes Open Access

Fukushima D., Shiokawa K., Otsuka Y., Kubota M., Yokoyama T., Nishioka M., Komonjinda S., Yatini C. Y.

EARTH PLANETS AND SPACE Vol. 69 2017.8

Equinoctial asymmetry in the zonal distribution of scintillation as observed by GPS receivers in Indonesia Open Access

Abadi P., Otsuka Y., Shiokawa K., Husin A., Liu Huixin, Saito S.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 122 ( 8 ) page： 8947-8958 2017.8

Sixteen year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at Shigaraki, Japan Open Access

Takeo D., Shiokawa K., Fujinami H., Otsuka Y., Matsuda T. S., Ejiri M. K., Nakamura T., Yamamoto M.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 122 ( 8 ) page： 8770-8780 2017.8

Sixteen-year variation of horizontal phase velocity and propagation direction of mesospheric and thermospheric waves in airglow images at Shigaraki Reviewed Open Access

Takeo, D, K. Shiokawa, H. Fujinami, Y. Otsuka, T. S. Matsuda, M. K. Ejiri, T. Nakamura, M. Yamamoto

Journal of Geophysical Research -Atmospheres Vol. 122 page： 8770-8780 2017.8

Conjugate observation of auroral finger-like structures by ground-based all-sky cameras and THEMIS satellites Open Access

Nishi Katsuki, Shiokawa Kazuo, Fruehauff Dennis

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 122 ( 7 ) page： 7291-7306 2017.7

Geospace exploration project: Arase (ERG) Open Access

E. R.G, Project Group, Y. Miyoshi, Y. Kasaba, I. Shinohara, T. Takashima, K. Asamura, H. Matsumoto, N. Higashio, T. Mitani, S. Kasahara, S. Yokota, S. Wang, Y. Kazama, Y. Kasahara, S. Yagitani, A. Matsuoka, H. Kojima, Y. Katoh, K. Shiokawa, K. Seki, M. Fujimoto, T. Ono

Journal of Physics: Conference Series Vol. 869 ( 1 ) 2017.7

Language：English Publishing type：Research paper (international conference proceedings)

© Published under licence by IOP Publishing Ltd. The ERG (Exploration of energization and Radiation in Geospace) is Japanese geospace exploration project. The project focuses on relativistic electron acceleration mechanism of the outer belt and dynamics of space storms in the context of the cross-energy coupling via wave-particle interactions. The project consists of the satellite observation team, the ground-based network observation team, and integrated-data analysis/simulation team. The satellite was launched on December 20 2016 and has been nicknamed, "Arase". This paper describes overview of the project and future plan for observations.

DOI： 10.1088/1742-6596/869/1/012095

On the effect of thermospheric neutral winds on post-midnight field-aligned irregularities at low latitudes Reviewed

Coordinated observations of postmidnight irregularities and thermospheric neutral winds and temperatures at low latitudes Open Access

Dao Tam, Otsuka Yuichi, Shiokawa Kazuo, Nishioka Michi, Yamamoto Mamoru, Buhari Suhaila M., Abdullah Mardina, Husin Asnawi

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 122 ( 7 ) page： 7504-7518 2017.7

Electron density variability of nighttime D region ionosphere in Vietnamese and Japanese sectors

Le Minh Tan, Shiokawa Kazuo, Nguyen Ngoc Thu, Tran Quoc Ha

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 122 ( 6 ) page： 6543-6551 2017.6

Simultaneous observations of magnetospheric ELF/VLF emissions in Canada, Finland, and Antarctica Open Access

Yonezu Yusuke, Shiokawa Kazuo, Connors Martin, Ozaki Mitsunori, Manninen Jyrki, Yamagishi Hisao, Okada Masaki

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 122 ( 6 ) page： 6442-6454 2017.6

First evidence of patchy flickering aurora modulated by multi-ion electromagnetic ion cyclotron waves Open Access

Fukuda Yoko, Kataoka Ryuho, Uchida Herbert Akihito, Miyoshi Yoshizumi, Hampton Donald, Shiokawa Kazuo, Ebihara Yusuke, Whiter Daniel, Iwagami Naomoto, Seki Kanako

GEOPHYSICAL RESEARCH LETTERS Vol. 44 ( 9 ) page： 3963-3970 2017.5

Contribution of storm time substorms to the prompt electric field disturbances in the equatorial ionosphere Open Access

Hui Debrup, Chakrabarty D., Sekar R., Reeves G. D., Yoshikawa A., Shiokawa K.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 122 ( 5 ) page： 5568-5578 2017.5

Effect of the Ionospheric Parameter Variations at Altitudes of 80-350 km on Diurnal Dynamics of the ULF Magnetic Field Spectra at Midlatitudes

Ermakova E. N., Kotik D. S., Pershin A. V., Pilipenko V. A., Shiokawa K.

RADIOPHYSICS AND QUANTUM ELECTRONICS Vol. 59 ( 12 ) page： 947-961 2017.5

Automatic selection of Dst storms and their seasonal variations in two versions of Dst in 50 years Open Access

Balan N., Tulasiram S., Kamide Y., Batista I. S., Souza J. R., Shiokawa K., Rajesh P. K., Victor N. J.

EARTH PLANETS AND SPACE Vol. 69 2017.4

Measurement of thermospheric temperatures using OMTI Fabry-Perot interferometers with 70-mm etalon Open Access

Nakamura Y., Shiokawa K., Otsuka Y., Oyama S., Nozawa S., Komolmis T., Komonjida S., Neudegg Dave, Yuile Colin, Meriwether J., Shinagawa H., Jin H.

EARTH PLANETS AND SPACE Vol. 69 2017.4

Large-scale traveling ionospheric disturbances observed by GPS dTEC maps over North and South America on Saint Patrick's Day storm in 2015 Open Access

Figueiredo C. A. O. B., Wrasse C. M., Takahashi H., Otsuka Y., Shiokawa K., Barros D.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 122 ( 4 ) page： 4755-4763 2017.4

A scheme for forecasting severe space weather

Balan N., Ebihara Y., Skoug R., Shiokawa K., Batista I. S., Ram S. Tulasi, Omura Y., Nakamura T., Fok M. -C.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 122 ( 3 ) page： 2824-2835 2017.3

Localized polar cap precipitation in association with nonstorm time airglow patches Open Access

Zou Ying, Nishimura Yukitoshi, Lyons Larry R., Shiokawa Kazuo

GEOPHYSICAL RESEARCH LETTERS Vol. 44 ( 2 ) page： 609-617 2017.1

Tam Dao, Yuichi Otsuka, Kazuo Shiokawa, Michi Nishioka, Mamoru Yamamoto, Suhaila M. Buhari, Mardina Abdullah, Asnawi Husin

2017 XXXIIND GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM OF THE INTERNATIONAL UNION OF RADIO SCIENCE (URSI GASS) Vol. 2017-January page： 1 - 4 2017

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

We investigated a post-midnight Field-Aligned Irregularities (FAIs) event observed with the Equatorial Atmosphere Radar (EAR) at Kototabang (0.2 degrees S, 100.3 degrees E, dip lat. 10.4 degrees S) in Indonesia on the night of 9 July 2010, using a comprehensive dataset of both neutral and plasma parameters. We compared FAI echoes collocated with 630 nm airglow depletion detected by an all-sky imager. The thermospheric neutral winds and temperatures obtained by a Fabry-Perot interferometer at Kototabang and the altitudes of F-layer (h'F) observed with ionosondes at Kototabang, Chiang Mai, and Chumphon were also examined. We found that the 3-m scale post-midnight FAIs occurred within plasma bubbles. The convergence of the equatorward neutral winds happened in this particular event related to midnight temperature maximum (MTM) and that the equatorward winds in both northern and southern hemispheres could be responsible for the growth of plasma bubbles around midnight. The uplift of F-layer at low latitudes could increase the growth rate of the Rayleigh-Taylor instability. Eastward electric currents driven by the equatorward winds could also contribute to the generation of the irregularities at post-midnight.

DOI： 10.23919/URSIGASS.2017.8105106

Other Link： http://orcid.org/0000-0002-4957-764X

The first long-term all-sky imager observation of lunar sodium tail Reviewed

Nishino Masaki N., Shiokawa Kazuo, Otsuka Yuichi

ICARUS Vol. 280 page： 199-204 2016.12

Ionospheric TEC Weather Map Over South America Reviewed Open Access

H. Takahashi, C. M. Wrasse, C. M. Denardini, M. B. Padua, E. R. de Paula, S. M. A. Costa, Y. Otsuka, K. Shiokawa, J. F. Galera Monico, A. Ivo, N. Sant'Anna

SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS Vol. 14 ( 11 ) page： 937 - 949 2016.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Ionospheric weather maps using the total electron content (TEC) monitored by ground-based Global Navigation Satellite Systems (GNSS) receivers over South American continent, TECMAP, have been operationally produced by Instituto Nacional de Pesquisas Espaciais's Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial) since 2013. In order to cover the whole continent, four GNSS receiver networks, (Rede Brasileiro de Monitoramento Continuo) RBMC/Brazilian Institute for Geography and Statistics, Low-latitude Ionospheric Sensor Network, International GNSS Service, and Red Argentina de Monitoreo Satelital Continuo, in total similar to 140 sites, have been used. TECMAPs with a time resolution of 10min are produced in 12h time delay. Spatial resolution of the map is rather low, varying between 50 and 500km depending on the density of the observation points. Large day-to-day variabilities of the equatorial ionization anomaly have been observed. Spatial gradient of TEC from the anomaly trough (total electron content unit, 1TECU=10(16)elm(-2) (TECU) <10) to the crest region (TECU>80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles, their seeding and development, could be monitored. This plasma density (spatial and temporal) variability causes not only the GNSS-based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC mapping becomes an important issue for space weather concern for high-technology positioning system and telecommunication.

DOI： 10.1002/2016SW001474

Heliospheric plasma sheet (HPS) impingement onto the magnetosphere as a cause of relativistic electron dropouts (REDs) via coherent EMIC wave scattering with possible consequences for climate change mechanisms Reviewed Open Access

Localized field-aligned currents in the polar cap associated with airglow patches Reviewed

Zou Ying, Nishimura Yukitoshi, Burchill Johnathan K., Knudsen David J., Lyons Larry R., Shiokawa Kazuo, Buchert Stephan, Chen Steve, Nicolls Michael J., Ruohoniemi J. Michael, McWilliams Kathryn A., Nishitani Nozomu

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 10 ) page： 10172-10189 2016.10

B. T. Tsurutani, R. Hajra, T. Tanimori, A. Takada, R. Bhanu, A. J. Mannucci, G. S. Lakhina, J. U. Kozyra, K. Shiokawa, L. C. Lee, E. Echer, R. V. Reddy, W. D. Gonzalez

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 10 ) page： 10130 - 10156 2016.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

A new scenario is presented for the cause of magnetospheric relativistic electron decreases (REDs) and potential effects in the atmosphere and on climate. High-density solar wind heliospheric plasmasheet (HPS) events impinge onto the magnetosphere, compressing it along with remnant noon-sector outer-zone magnetospheric similar to 10-100 keV protons. The betatron accelerated protons generate coherent electromagnetic ion cyclotron (EMIC) waves through a temperature anisotropy (T-perpendicular to/T-|| > 1) instability. The waves in turn interact with relativistic electrons and cause the rapid loss of these particles to a small region of the atmosphere. A peak total energy deposition of similar to 3 x 10(20) ergs is derived for the precipitating electrons. Maximum energy deposition and creation of electron-ion pairs at 30-50 km and at > 30 km altitude are quantified. We focus the readers' attention on the relevance of this present work to two climate change mechanisms. Wilcox et al. (1973) noted a correlation between solar wind heliospheric current sheet (HCS) crossings and high atmospheric vorticity centers at 300 mb altitude. Tinsley et al. (1994) has constructed a global circuit model which depends on particle precipitation into the atmosphere. Other possible scenarios potentially affecting weather/climate change are also discussed.

DOI： 10.1002/2016JA022499

Spectral characteristics of steady quiet-time EMIC waves observed at geosynchronous orbit Reviewed Open Access

Kim Khan-Hyuk, Park Jong-Sun, Omura Yoshiharu, Shiokawa Kazuo, Lee Dong-Hun, Kim Gi-Jeong, Jin Ho, Lee Ensang, Kwon Hyuck-Jin

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 9 ) page： 8640-8660 2016.9

Quasi-periodic rapid motion of pulsating auroras Reviewed Open Access

Fukuda Yoko, Kataoka Ryuho, Miyoshi Yoshizumi, Katoh Yuto, Nishiyama Takanori, Shiokawa Kazuo, Ebihara Yusuke, Hampton Donald, Iwagami Naomoto

POLAR SCIENCE Vol. 10 ( 3 ) page： 183-191 2016.9

A proposal on the study of solar-terrestrial coupling processes with atmospheric radars and ground-based observation network Reviewed Open Access

Tsuda Toshitaka, Yamamoto Mamoru, Hashiguchi Hiroyuki, Shiokawa Kazuo, Ogawa Yasunobu, Nozawa Satonori, Miyaoka Hiroshi, Yoshikawa Akimasa

RADIO SCIENCE Vol. 51 ( 9 ) page： 1587-1599 2016.9

Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes Reviewed Open Access

M. Ozaki, K. Shiokawa, Y. Miyoshi, R. Kataoka, S. Yagitani, T. Inoue, Y. Ebihara, C. -W Jun, R. Nomura, K. Sakaguchi, Y. Otsuka, M. Shoji, I. Schofield, M. Connors, V. K. Jordanova

GEOPHYSICAL RESEARCH LETTERS Vol. 43 ( 15 ) page： 7859 - 7866 2016.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave-particle interactions at subauroral latitudes, high-time-resolution (1/8s) images of proton-induced N-2(+) emissions were recorded using a new electron multiplying charge-coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising-tone elements with a spacing for each element of 100s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensity showed a similar repetition period of 100s and an unpredicted fast modulation of a few tens of seconds. These results indicate that PPA is generated by pitch angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator.

DOI： 10.1002/2016GL070008

Direct observational evidence for the merging of equatorial plasma bubbles Reviewed

V. L. Narayanan, S. Gurubaran, K. Shiokawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 8 ) page： 7923 - 7931 2016.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

In this work we present direct ground-based observational evidence for the merging of individual equatorial plasma bubbles (EPBs) obtained through the imaging of OI 630.0 nm airglow. Three potential mechanisms have been identified: (1) One of the EPBs tilts and reaches location of the adjacent growing EPB finally merging with it. (2) Some of the branches of an EPB arising from secondary instabilities reach out to adjacent EPB and merge with it. (3) The eastward zonal drift of the EPB on the eastern side slows down while the adjacent EPB on the western side drifts relatively faster and catches up. In one of the cases, a branch of an EPB was observed to get interchanged with another EPB as a result of merging and consequent pinching off from the parent EPB.

DOI： 10.1002/2016JA022861

Shrinking equatorial plasma bubbles Reviewed Open Access

V. L. Narayanan, S. Gurubaran, K. Shiokawa, K. Emperumal

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 7 ) page： 6924 - 6935 2016.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

The formation of equatorial plasma bubbles (EPBs) associated with spread F irregularities are fairly common phenomenon in the postsunset equatorial ionosphere. These bubbles grow as a result of eastward polarization electric field resulting in upward ExB drift over the dip equator. As they grow they are also mapped to low latitudes along magnetic field lines. The EPBs are often observed as airglow depletions in the images of OI 630nm emission. On occasions the growth of the features over the dip equator is observed as poleward extensions of the depletions in all-sky images obtained from low latitudes. Herein, we present interesting observations of decrease in the latitudinal extent of the EPBs corresponding to a reduction in their apex altitudes over the dip equator. Such observations indicate that these bubbles not only grow but also shrink on occasions. These are the first observations of shrinking EPBs. The observations discussed in this work are based on all-sky airglow imaging observations of OI 630.0nm emission made from Panhala (11.1 degrees N dip latitude). In addition, ionosonde observations made from dip equatorial site Tirunelveli (1.1 degrees N dip latitude) are used to understand the phenomenon better. The analysis indicates that the speed of shrinking occurring in the topside is different from the bottomside vertical drifts. When the EPBs shrink, they might decay before sunrise hours.

DOI： 10.1002/2016JA022633

ELF/VLF wave propagation at subauroral latitudes: Conjugate observation between the ground and Van Allen Probes A Reviewed Open Access

Martinez-Calderon Claudia, Shiokawa Kazuo, Miyoshi Yoshizumi, Keika Kunihiro, Ozaki Mitsunori, Schofield Ian, Connors Martin, Kletzing Craig, Hanzelka Miroslav, Santolik Ondrej, Kurth William S.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 6 ) page： 5384-5393 2016.6

Special issue "The 12th International Conference on Substorms"

Shiokawa Kazuo, Fok Mei-Ching, Fujimoto Masaki

EARTH PLANETS AND SPACE Vol. 68 2016.5

Possible generation mechanisms for Pc1 pearl structures in the ionosphere based on 6 years of ground observations in Canada, Russia, and Japan Reviewed Open Access

Jun Chae-Woo, Shiokawa Kazuo, Connors Martin, Schofield Ian, Poddelsky Igor, Shevtsov Boris

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 5 ) page： 4409-4424 2016.5

An evidence for prompt electric field disturbance driven by changes in the solar wind density under northward IMF B-z condition Reviewed Open Access

Diptiranjan Rout, D. Chakrabarty, R. Sekar, G. D. Reeves, J. M. Ruohoniemi, Tarun K. Pant, B. Veenadhari, K. Shiokawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 5 ) page： 4800 - 4810 2016.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Before the onset of a geomagnetic storm on 22 January 2012 (Ap = 24), an enhancement in solar wind number density from 10/cm(3) to 22/cm(3) during 0440-0510UT under northward interplanetary magnetic field (IMF B-z) condition is shown to have enhanced the high-latitude ionospheric convection and also caused variations in the geomagnetic field globally. Conspicuous changes in X are observed not only at longitudinally separated low-latitude stations over Indian (prenoon), South American (midnight), Japanese (afternoon), Pacific (afternoon) and African (morning) sectors but also at latitudinally separated stations located over high and middle latitudes. The latitudinal variation of the amplitude of the X during 0440-0510UT is shown to be consistent with the characteristics of prompt penetration electric field disturbances. Most importantly, the density pulse event caused enhancements in the equatorial electrojet strength and the peak height of the F layer (h(m)F(2)) over the Indian dip equatorial sector. Further, the concomitant enhancements in electrojet current and F layer movement over the dip equator observed during this space weather event suggest a common driver of prompt electric field disturbance at this time. Such simultaneous variations are found to be absent during magnetically quiet days. In absence of significant change in solar wind velocity and magnetospheric substorm activity, these observations point toward perceptible prompt electric field disturbance over the dip equator driven by the overcompression of the magnetosphere by solar wind density enhancement.

DOI： 10.1002/2016JA022475

Coordinated observations of F region 3m field-aligned plasma irregularities associated with medium-scale traveling ionospheric disturbances Reviewed

Lower thermospheric wind variations in auroral patches during the substorm recovery phase Reviewed Open Access

Oyama Shin-ichiro, Shiokawa Kazuo, Miyoshi Yoshizumi, Hosokawa Keisuke, Watkins Brenton J., Kurihara Junichi, Tsuda Takuo T., Fallen Christopher T.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 4 ) page： 3564-3577 2016.4

F. F. Lin, C. Y. Wang, C. L. Su, K. Shiokawa, S. Saito, Y. H. Chu

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 4 ) page： 3750 - 3766 2016.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Three meter field-aligned irregularities (3m FAIs) associated with medium-scale traveling ionospheric disturbances (MSTIDs) that occurred on 5 February 2008 were observed by using the Chung-Li 52MHz coherent scatter radar. Interferometry measurements show that the plasma structures responsible for the 3m FAI echoes are in a clumpy shape with a horizontal dimension of about 10-78km in a height range of 220-300km. In order to investigate the dynamic behaviors of the plasma irregularities at different scales in the bottomside of F region, the VHF radar echo structures from the 3m FAIs combined with the 630 nm airglow images provided by the Yonaguni all-sky imager are compared and analyzed. The results show that the radar echoes were located at the west edge of the depletion zones of the 630 nm airglow image of the MSTIDs. The bulk echo structures of the 3m FAIs drifted eastward at a mean trace velocity of about 30m/s that is in general agreement with the zonal trace velocity of the MSTIDs shown in the 630nm airglow images. These results suggest that the observed F region 3m FAIs for the present case can be regarded as the targets that are frozen in the local region of theMSTIDs. In addition, the radar-observed 3mFAI echo intensity and spectral width bear high correlations to the percentage variations of the 630nm emission intensity. These results seem to suggest that through the nonlinear turbulence cascade process, theMSTID-associated 3mFAIs are very likely generated from the kilometer-scale plasma irregularities with large amplitude excited by the gradient drift instability.

DOI： 10.1002/2016JA022511

Special issue "International CAWSES-II Symposium"

Yamamoto Mamoru, Shiokawa Kazuo, Nakamura Takuji, Gopalswamy Nat

EARTH PLANETS AND SPACE Vol. 68 2016.2

Altitude development of postmidnight F region field-aligned irregularities observed using Equatorial Atmosphere Radar in Indonesia Reviewed Open Access

Tam Dao, Otsuka Yuichi, Shiokawa Kazuo, Ram S. Tulasi, Yamamoto Mamoru

GEOPHYSICAL RESEARCH LETTERS Vol. 43 ( 3 ) page： 1015-1022 2016.2

Longitudinal frequency variation of long-lasting EMIC Pc1-Pc2 waves localized in the inner magnetosphere Reviewed Open Access

K. -H. Kim, K. Shiokawa, I. R. Mann, J. -S. Park, H. -J. Kwon, K. Hyun, H. Jin, M. Connors

GEOPHYSICAL RESEARCH LETTERS Vol. 43 ( 3 ) page： 1039 - 1046 2016.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Long-lasting (>20h) electromagnetic ion cyclotron (EMIC) Pc1-Pc2 waves were observed by the Athabasca (L =approximate to 4.6) induction magnetometer and Canadian Array for Realtime Investigations of Magnetic Activity (L =approximate to 4-6) fluxgate magnetometers on 5 April 2007. These waves showed a systematic frequency change with local time, the minimum frequency near dusk, and the maximum frequency near dawn. Assuming the plasmapause as a potential source region of the waves, we estimated the plasmapause location from localized proton enhancement (LPE) events observed at NOAA-Polar Orbiting Environmental Satellites and METOP-2 satellites. We found that the longitudinal frequency variation of EMIC waves has a clear correlation with the estimated plasmapause location and that the waves are in the frequency band between the equatorial helium and oxygen gyrofrequencies at the estimated plasmapause. With our analysis results we suggest that the LPE events are caused by wave-particle interaction with the helium band EMIC waves generated near the plasmapause.

DOI： 10.1002/2015GL067536

EMIC waves observed at geosynchronous orbit under quiet geomagnetic conditions (Kp1) Reviewed Open Access

J. -S. Park, K. -H. Kim, K. Shiokawa, D. -H. Lee, E. Lee, H. -J. Kwon, H. Jin, G. Jee

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 2 ) page： 1377 - 1390 2016.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We statistically study the local time distribution of the helium band electromagnetic ion cyclotron (EMIC) waves observed at geosynchronous orbit when geomagnetic activity was low (Kp 1). In order to identify the geosynchronous EMIC waves, we use high time resolution magnetic field data acquired from GOES 10, 11, and 12 over a 2year period from 2007 and 2008 and examine the local time distribution of EMIC wave events. Unlike previous studies, which reported high EMIC wave occurrence in the postnoon sector with a peak around 1500-1600 magnetic local time (MLT) during magnetically disturbed times (i.e., storm and/or substorm), we observed that quiet time EMIC waves mostly occur in a region from morning (approximate to 0600MLT) to afternoon (approximate to 1600MLT) with a peak around 1100-1200MLT. To investigate whether the quiet time EMIC wave occurrence has a causal relationship with magnetospheric convection enhancement or solar wind dynamic pressure variations, we performed a superposed epoch analysis of solar wind parameters (solar wind speed, density, dynamic pressure, and interplanetary magnetic field B-z) and geomagnetic indices (AE and SYM-H). From the superposed epoch analysis we found that solar wind dynamic pressure variation is a more important parameter than AE and SYM-H for quiet time EMIC wave occurrence.

DOI： 10.1002/2015JA021968

Pulsating proton aurora caused by rising tone Pc1 waves Reviewed Open Access

R. Nomura, K. Shiokawa, Y. Omura, Y. Ebihara, Y. Miyoshi, K. Sakaguchi, Y. Otsuka, M. Connors

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 2 ) page： 1608 - 1618 2016.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We found rising tone emissions with a dispersion of approximate to 1Hz per several tens of seconds in the dynamic spectrum of a Pc1 geomagnetic pulsation (Pc1) observed on the ground. These Pc1 rising tones were successively observed over approximate to 30min from 0250UT on 14 October 2006 by an induction magnetometer at Athabasca, Canada (54.7 degrees N, 246.7 degrees E, magnetic latitude 61.7 degrees N). Simultaneously, a Time History of Events and Macroscale Interactions during Substorms panchromatic (THEMIS) all-sky camera detected pulsations of an isolated proton aurora with a period of several tens of seconds, approximate to 10% variations in intensity, and fine structures of 3 degrees in magnetic longitudes. The pulsations of the proton aurora close to the zenith of ATH have one-to-one correspondences with the Pc1 rising tones. This suggests that these rising tones scatter magnetospheric protons intermittently at the equatorial region. The radial motion of the magnetospheric source, of which the isolated proton aurora is a projection, can explain the central frequency increase of Pc1, but not the shorter period (tens of seconds) frequency increase of approximate to 1Hz in Pc1 rising tones. We suggest that EMIC-triggered emissions generate the frequency increase of Pc1 rising tones on the ground and that they also cause the Pc1 pearl structure, which has a similar characteristic time.

DOI： 10.1002/2015JA021681

Duskside enhancement of equatorial zonal electric field response to convection electric fields during the St. Patrick's Day storm on 17 March 2015 Reviewed Open Access

S. Tulasi Ram, T. Yokoyama, Y. Otsuka, K. Shiokawa, S. Sripathi, B. Veenadhari, R. Heelis, K. K. Ajith, V. S. Gowtam, S. Gurubaran, P. Supnithi, M. Le Huy

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 121 ( 1 ) page： 538 - 548 2016.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

The equatorial zonal electric field responses to prompt penetration of eastward convection electric fields (PPEF) were compared at closely spaced longitudinal intervals at dusk to premidnight sectors during the intense geomagnetic storm of 17 March 2015. At dusk sector (Indian longitudes), a rapid uplift of equatorial F layer to >550km and development of intense equatorial plasma bubbles (EPBs) were observed. These EPBs were found to extend up to 27.13 degrees N and 25.98 degrees S magnetic dip latitudes indicating their altitude development to similar to 1670km at apex. In contrast, at few degrees east in the premidnight sector (Thailand-Indonesian longitudes), no significant height rise and/or EPB activity has been observed. The eastward electric field perturbations due to PPEF are greatly dominated at dusk sector despite the existence of background westward ionospheric disturbance dynamo (IDD) fields, whereas they were mostly counter balanced by the IDD fields in the premidnight sector. In situ observations from SWARM-A and SWARM-C and Communication/Navigation Outage Forecasting System satellites detected a large plasma density depletion near Indian equatorial region due to large electrodynamic uplift of F layer to higher than satellite altitudes. Further, this large uplift is found to confine to a narrow longitudinal sector centered on sunset terminator. This study brings out the significantly enhanced equatorial zonal electric field in response to PPEF that is uniquely confined to dusk sector. The responsible mechanisms are discussed in terms of unique electrodynamic conditions prevailing at dusk sector in the presence of convection electric fields associated with the onset of a substorm under southward interplanetary magnetic field B-z.

DOI： 10.1002/2015JA021932

Polar cap precursor of nightside auroral oval intensifications using polar cap arcs Reviewed Open Access

Zou Ying, Nishimura Yukitoshi, Lyons Larry R., Donovan Eric F., Shiokawa Kazuo, Ruohoniemi J. Michael, McWilliams Kathryn A., Nishitani Nozomu

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 12 ) page： 10698-10711 2015.12

Isolated Proton Auroras and Pc1/EMIC Waves at Subauroral Latitudes Reviewed

Kaori Sakaguchi, Kazuo Shiokawa, Yoshizumi Miyoshi, Martin Connors

Auroral Dynamics and Space Weather page： 59 - 70 2015.11

Language：English Publishing type：Part of collection (book) Publisher：Wiley Blackwell

Isolated proton aurora (IPA) in the subauroral ionosphere is created by energetic proton precipitation through wave-particle interactions with electromagnetic ion cyclotron (EMIC) waves in the conjugate inner magnetosphere. In this study, spatial distribution and occurrence probability of IPAs were statistically investigated as a proxy for regions of EMIC wave occurrence using ground-based imaging data during 2006-2012 at Athabasca, Canada. The 7-year average of the IPA occurrence probability over the total observation interval was estimated to be 0.83%, and a factor of 5 change was found between maximum and minimum years. Local time (between 16 and 06 MLT) distribution shows double peaks at premidnight and at dusk. The occurrence probability increases with Kp, and the MLT location tends to shift duskward. The statistical distribution of IPA size shows a clear peak at a spatial size of 10,000 km2, and latitudinal and longitudinal lengths have peaks at 56 and 340 km, respectively, at the ionospheric altitude. The equatorial projections of IPA source locations and two-dimensional (2D) structures are estimated by magnetic field tracing. These spatial structures are essential to quantitatively estimate the loss rate of energetic particles, contributing to space weather studies.

DOI： 10.1002/9781118978719.ch5

A direct link between chorus emissions and pulsating aurora on timescales from milliseconds to minutes: A case study at subauroral latitudes Reviewed Open Access

Ozaki Mitsunori, Yagitani Satoshi, Sawai Kaoru, Shiokawa Kazuo, Miyoshi Yoshizumi, Kataoka Ryuho, Ieda Akimasa, Ebihara Yusuke, Connors Martin, Schofield Ian, Katoh Yuto, Otsuka Yuichi, Sunagawa Naoki, Jordanova Vania K.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 11 ) page： 9617-9631 2015.11

Coordinated airglow observations between IMAP/VISI and a ground-based all-sky imager on concentric gravity wave in the mesopause Reviewed Open Access

S. Perwitasari, T. Sakanoi, A. Yamazaki, Y. Otsuka, Y. Hozumi, Y. Akiya, A. Saito, K. Shiokawa, S. Kawamura

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 11 ) page： 9706 - 9721 2015.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We present a study of concentric gravity waves (CGWs) event from the coordinated observation between Ionosphere, Mesosphere, upper Atmosphere, and Plasmasphere mapping (IMAP)/Visible and near-Infrared Spectral Imager (VISI), all-sky camera at Rikubetsu, Multi-functional Transport Satellite (MTSAT), Tropical Rainfall Measuring Mission, and MF radar at Wakkanai combined with Modern-Era Retrospective Analysis for Research and Application data. IMAP/VISI is the first space-based imager that capable of imaging the airglow in the mesosphere and lower thermosphere region in the nadir-looking direction. Therefore, it has a unique ability to observe a great extend of CGWs propagation. Arc-like shaped, part of CGWs pattern was observed around themesopause (similar to 95 km) in the O-2 762 nm airglow emission obtained by IMAP/VISI at 1204 UT on 18 October 2012. Similar patterns were also observed by the all-sky imager at Rikubetsu (43.5 degrees N, 143.8 degrees E) in OI 557.7 nm and OH band airglow emissions from similar to 1100 to 1200 UT. Horizontal wavelengths of the observed small-scale gravity waves are similar to 50 km (OH band and OI 557.7nm) and similar to 67 km (O-2 762 nm). The source is suggested to be a deep convective activity over Honshu Island which likely was an enhanced convective activity related to a typhoon in the south of Japan. The data showed that the CGWs could propagate up to similar to 1400-1500km horizontally from the source to the mesopause but not farther away. Using atmospheric temperature profiles obtained by Thermospheric Ionosphere Mesosphere Energetics Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry, we conclude that this long-distance propagation of the waves could be caused by thermal duct in the middle atmosphere. The arc-like shaped instead of full circle pattern points out that the wind filtering effect is significant for the particular direction of wave propagation.

DOI： 10.1002/2015JA021424

Spatiotemporally resolved electrodynamic properties of a Sun-aligned arc over Resolute Bay Reviewed Open Access

G. W. Perry, H. Dahlgren, M. J. Nicolls, M. Zettergren, J. -P. St-Maurice, J. L. Semeter, T. Sundberg, K. Hosokawa, K. Shiokawa, S. Chen

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 11 ) page： 9977 - 9987 2015.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Common volume measurements by the Resolute Bay Incoherent Scatter Radar-North (RISR-N) and Optical Mesosphere and Thermosphere Imagers (OMTI) have been used to clarify the electrodynamic structure of a Sun-aligned arc in the polar cap. The plasma parameters of the dusk-to-dawn drifting arc and surrounding ionosphere are extracted using the volumetric imaging capabilities of RISR-N. Multipoint line-of-sight RISR-N measurements of the plasma drift are inverted to construct a time sequence of the electric field and field-aligned current system of the arc. Evidence of dramatic electrodynamic and plasma structuring of the polar cap ionosphere due to the arc is described. One notable feature of the arc is a meridionally extended plasma density depletion on its leading edge, located partially within a downward field-aligned current region. The depletion is determined to be a by-product of enhanced chemical recombination operating on a time scale of 15 min. A similarly shaped electric field structure of over 100 mV/m and line-of-sight ion temperatures nearing 3000 K were collocated with the depletion.

DOI： 10.1002/2015JA021790

Statistical study of ELF/VLF emissions at subauroral latitudes in Athabasca, Canada Reviewed Open Access

Martinez-Calderon Claudia, Shiokawa Kazuo, Miyoshi Yoshizumi, Ozaki Mitsunori, Schofield Ian, Connors Martin

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 10 ) page： 8455-8469 2015.10

On the formation and origin of substorm growth phase/onset auroral arcs inferred from conjugate space-ground observations Reviewed Open Access

T. Motoba, S. Ohtani, B. J. Anderson, H. Korth, D. Mitchell, L. J. Lanzerotti, K. Shiokawa, M. Connors, C. A. Kletzing, G. D. Reeves

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 10 ) page： 8707 - 8722 2015.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Magnetotail processes and structures related to substorm growth phase/onset auroral arcs remain poorly understood mostly due to the lack of adequate observations. In this study we make a comparison between ground-based optical measurements of the premidnight growth phase/onset arcs at subauroral latitudes and magnetically conjugate measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) at 780km in altitude and by the Van Allen Probe B (RBSP-B) spacecraft crossing L values of 5.0-5.6 in the premidnight inner tail region. The conjugate observations offer a unique opportunity to examine the detailed features of the arc location relative to large-scale Birkeland currents and of the magnetospheric counterpart. Our main findings include (1) at the early stage of the growth phase the quiet auroral arc emerged 4.3 degrees equatorward of the boundary between the downward Region 2 (R2) and upward Region 1 (R1) currents; (2) shortly before the auroral breakup (poleward auroral expansion) the latitudinal separation between the arc and the R1/R2 demarcation narrowed to 1.0 degrees; (3) RBSP-B observed a magnetic field signature of a local upward field-aligned current (FAC) connecting the arc with the near-Earth tail when the spacecraft footprint was very close to the arc; and (4) the upward FAC signature was located on the tailward side of a local plasma pressure increase confined near L5.2-5.4. These findings strongly suggest that the premidnight arc is connected to highly localized pressure gradients embedded in the near-tail R2 source region via the local upward FAC.

DOI： 10.1002/2015JA021676

Multi-instrument, high-resolution imaging of polar cap patch transportation Reviewed Open Access

E. G. Thomas, K. Hosokawa, J. Sakai, J. B. H. Baker, J. M. Ruohoniemi, S. Taguchi, K. Shiokawa, Y. Otsuka, A. J. Coster, J. -P. St.-Maurice, K. A. McWilliams

RADIO SCIENCE Vol. 50 ( 9 ) page： 904 - 915 2015.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Transionospheric radio signals in the high-latitude polar cap are susceptible to degradation when encountering sharp electron density gradients associated with discrete plasma structures, or patches. Multi-instrument measurements of polar cap patches are examined during a geomagnetic storm interval on 22 January 2012. For the first time, we monitor the transportation of patches with high spatial and temporal resolution across the polar cap for 1-2 h using a combination of GPS total electron content (TEC), all-sky airglow imagers (ASIs), and Super Dual Auroral Radar Network (SuperDARN) HF radar backscatter. Simultaneous measurements from these data sets allow for continuous tracking of patch location, horizontal extent, and velocity despite adverse observational conditions for the primary technique (e.g., sunlit regions in the ASI data). Spatial collocation between patch-like features in relatively coarse but global GPS TEC measurements and those mapped by high-resolution ASI data was very good, indicating that GPS TEC can be applied to track patches continuously as they are transported across the polar cap. In contrast to previous observations of cigar-shaped patches formed under weakly disturbed conditions, the relatively narrow dawn-dusk extent of patches in the present interval (500-800 km) suggests association with a longitudinally confined plasma source region, such as storm-enhanced density (SED) plume. SuperDARN observations show that the backscatter power enhancements corresponded to the optical patches, and for the first time we demonstrate that the motion of the optical patches was consistent with background plasma convection velocities.

DOI： 10.1002/2015RS005672

Statistical study of auroral fragmentation into patches Reviewed Open Access

Hashimoto Ayumi, Shiokawa Kazuo, Otsuka Yuichi, Oyama Shin-ichiro, Nozawa Satonori, Hori Tomoaki, Lester Mark, Johnsen Magnar Gullikstad

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 8 ) page： 6207-6217 2015.8

Plasma bubble monitoring by TEC map and 630 nm airglow image Reviewed Open Access

H. Takahashi, C. M. Wrasse, Y. Otsuka, A. Ivo, V. Gomes, I. Paulino, A. F. Medeiros, C. M. Denardini, N. Sant'Anna, K. Shiokawa

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 130 page： 151 - 158 2015.8

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Equatorial ionosphere plasma bubbles over the South American continent were successfully observed by mapping the total electron content (TECMAP) using data provided by ground-based GNSS receiver networks. The TECMAP could cover almost all of the continent within 4000 km distance in longitude and latitude, monitoring TEC variability continuously with a time resolution of 10 min. Simultaneous observations of OI 630 nm all-sky image at Cachoeira Paulista (22.7 degrees S, 45.0 degrees W) and Cariri (7.4 degrees S, 36.5 degrees W) were used to compare the bubble structures. The spatial resolution of the TECMAP varied from 50 km to 1000 km, depending on the density of the observation sites. On the other hand, optical imaging has a spatial resolution better than 15 km, depicting the fine structure of the bubbles but covering a limited area (similar to 1600 km diameter). TECMAP has an advantage in its spatial coverage and the continuous monitoring (day and night) form. The initial phase of plasma depletion in the post-sunset equatorial ionization anomaly (PS-EIA) trough region, followed by development of plasma bubbles in the crest region, could be monitored in a progressive way over the magnetic equator. In December 2013 to January 2014, periodically spaced bubble structures were frequently observed. The longitudinal spacing between the bubbles was around 600-800 km depending on the day. The periodic form of plasma bubbles may suggest a seeding process related to the solar terminator passage in the ionosphere. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jastp.2015.06.003

Van Allen probes, NOAA, GOES, and ground observations of an intense EMIC wave event extending over 12 h in magnetic local time Reviewed Open Access

M. J. Engebretson, J. L. Posch, J. R. Wygant, C. A. Kletzing, M. R. Lessard, C. -L. Huang, H. E. Spence, C. W. Smith, H. J. Singer, Y. Omura, R. B. Horne, G. D. Reeves, D. N. Baker, M. Gkioulidou, K. Oksavik, I. R. Mann, T. Raita, K. Shiokawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 7 ) page： 5465 - 5488 2015.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Although most studies of the effects of electromagnetic ion cyclotron (EMIC) waves on Earth's outer radiation belt have focused on events in the afternoon sector in the outer plasmasphere or plume region, strong magnetospheric compressions provide an additional stimulus for EMIC wave generation across a large range of local times and L shells. We present here observations of the effects of a wave event on 23 February 2014 that extended over 8h in UT and over 12h in local time, stimulated by a gradual 4h rise and subsequent sharp increases in solar wind pressure. Large-amplitude linearly polarized hydrogen band EMIC waves (up to 25nT p-p) appeared for over 4h at both Van Allen Probes, from late morning through local noon, when these spacecraft were outside the plasmapause, with densities similar to 5-20cm(-3). Waves were also observed by ground-based induction magnetometers in Antarctica (near dawn), Finland (near local noon), Russia (in the afternoon), and in Canada (from dusk to midnight). Ten passes of NOAA-POES and METOP satellites near the northern foot point of the Van Allen Probes observed 30-80keV subauroral proton precipitation, often over extended L shell ranges; other passes identified a narrow L shell region of precipitation over Canada. Observations of relativistic electrons by the Van Allen Probes showed that the fluxes of more field-aligned and more energetic radiation belt electrons were reduced in response to both the emission over Canada and the more spatially extended emission associated with the compression, confirming the effectiveness of EMIC-induced loss processes for this event.

DOI： 10.1002/2015JA021227

Three different types of electric field disturbances affecting equatorial ionosphere during a long-duration prompt penetration event Reviewed

Resonance structure and mode transition of quarter-wave ULF pulsations around the dawn terminator Reviewed Open Access

Obana Yuki, Waters Colin L., Sciffer Murray D., Menk Frederick W., Lysak Robert L., Shiokawa Kazuo, Hurst Anthony W., Petersen Tanja

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 6 ) page： 4194-4212 2015.6

D. Chakrabarty, Diptiranjan Rout, R. Sekar, R. Narayanan, G. D. Reeves, Tarun K. Pant, B. Veenadhari, K. Shiokawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 6 ) page： 4993 - 5008 2015.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Coordinated digisonde and OI 630.0nm airglow observations from Thumba (TVM), an Indian dip equatorial station, in conjunction with magnetic and geosynchronous particle flux measurements, reveal three different types of electric field disturbances in the equatorial ionosphere-thermosphere system (ITS) occurring in succession over a period of 6h on a single night (22-23 January,2012; A(p) = 24). These include (1) westward electric field perturbations owing to a pseudo-breakup and a substorm event, each lasting for about 30min; (2) eastward electric field perturbations continuing for about an hour, owing to the southward excursion of Z component of interplanetary magnetic field (B-z); and (3) DP2-type fluctuating (period approximate to 40min) electric field perturbation sustaining for about 4h. The pseudo-breakup and the fully grown substorm events are found to be longitudinally localized and different in terms of response in the westward auroral electrojet index (AL) as well as geosynchronous electron/proton injections. The polarity of the prompt penetration of interplanetary electric field that affects the equatorial ionosphere is observed to be eastward during 2100-2200 IST (Indian Standard Time) which is observationally sparse but consistent with modeling studies. Interestingly, on the same night, DP2-type electric field fluctuations with approximate to 40min periodicity and occasional eastward polarity (akin to daytime) are also found to affect the equatorial ITS for about 4h (2200-0200 IST). The case study, thus, brings out different processes that constitute a long duration prompt penetration event which, otherwise, would have been categorized as a single event.

DOI： 10.1002/2014JA020759

Geomagnetically conjugate observation of plasma bubbles and thermospheric neutral winds at low latitudes Reviewed

Localized polar cap flow enhancement tracing using airglow patches: Statistical properties, IMF dependence, and contribution to polar cap convection Reviewed

Zou Ying, Nishimura Yukitoshi, Lyons Larry R., Shiokawa Kazuo, Donovan Eric F., Ruohoniemi J. Michael, McWilliams Kathryn A., Nishitani Nozomu

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 5 ) page： 4064-4078 2015.5

Airglow-imaging observation of plasma bubble disappearance at geomagnetically conjugate points Reviewed Open Access

Shiokawa Kazuo, Otsuka Yuichi, Lynn Kenneth J. W., Wilkinson Philip, Tsugawa Takuya

EARTH PLANETS AND SPACE Vol. 67 ( 43 ) page： 1-12 2015.3

D. Fukushima, K. Shiokawa, Y. Otsuka, M. Nishioka, M. Kubota, T. Tsugawa, T. Nagatsuma, S. Komonjinda, C. Y. Yatini

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 3 ) page： 2222 - 2231 2015.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

This is the first paper that reports simultaneous observations of zonal drift of plasma bubbles and the thermospheric neutral winds at geomagnetically conjugate points in both hemispheres. The plasma bubbles were observed in the 630nm nighttime airglow images taken by using highly sensitive all-sky airglow imagers at Kototabang, Indonesia (geomagnetic latitude (MLAT): 10.0 degrees S), and Chiang Mai, Thailand (MLAT: 8.9 degrees N), which are nearly geomagnetically conjugate stations, for 7h from 13 to 20UT (from 20 to 03LT) on 5 April 2011. The bubbles continuously propagated eastward with velocities of 100-125m/s. The 630nm images at Chiang Mai and those mapped to the conjugate point of Kototabang fit very well, which indicates that the observed plasma bubbles were geomagnetically connected. The eastward thermospheric neutral winds measured by two Fabry-Perot interferometers were 70-130m/s at Kototabang and 50-90m/s at Chiang Mai. We compared the observed plasma bubble drift velocity with the velocity calculated from the observed neutral winds and the model conductivity, to investigate the F region dynamo contribution to the bubble drift velocity. The estimated drift velocities were 60-90% of the observed velocities of the plasma bubbles, suggesting that most of the plasma bubble velocity can be explained by the F region dynamo effect.

DOI： 10.1002/2014JA020398

CDF data archive and integrated data analysis platform for ERG-related ground data developed by ERG Science Center (ERG-SC) Reviewed

Hori, T, Y. Miyashita, Y. Miyoshi, K. Seki, T. Segawa, Y.-M. Tanaka, K. Keika, M. Shoji, I. Shinohara, K. Shiokawa, Y. Otsuka, S. Abe, A. Yoshikawa, K. Yumoto, Y. Obana, N. Nishitani, A. S. Yukimatu, T. Nagatsuma, M. Kunitake, K. Hosokawa, Y. Ogawa, K. T. Murata, M. Nose, H. Kawano, T. Sakanoi

J. Sp. Sci. Info. Jpn. Vol. 4 (JAXA-RR-14-009) page： 75 - 89 2015.3

Language：English Publishing type：Research paper (scientific journal)

The Exploration of energization and Radiation in Geospace project Science Center (ERG-SC) has developed the science data file archive and integrated data analysis tool for the ground network observation data of the ERG project. We have organized data design consortiums to develop and elaborate the standard metadata and data variable sets for each type of the ERG-related ground data being archived as Common Data Format (CDF) files. The integrated data analysis software for the project has also been developed on the basis of the Space Physics Environment Data Analysis Software (SPEDAS) which works in concert with the CDF data file repository. The software tools, which are provided as plug-in libraries for SPEDAS, are made available to the international science community so that scientists and students are ready to proceed to integrated studies combining the ground data with other satellite and simulation data seamlessly. The integrated data analysis software can make scientific activities more productive and help the ERG project achieve the scientific goals.

Polarization analysis of VLF/ELF waves observed at subauroral latitudes during the VLF-CHAIN campaign Reviewed Open Access

Martinez-Calderon Claudia, Shiokawa Kazuo, Miyoshi Yoshizumi, Ozaki Mitsunori, Schofield Ian, Connors Martin

EARTH PLANETS AND SPACE Vol. 67 2015.2

The geospace response to variable inputs from the lower atmosphere: a review of the progress made by Task Group 4 of CAWSES-II Reviewed Open Access

Oberheide Jens, Shiokawa Kazuo, Gurubaran Subramanian, Ward William E., Fujiwara Hitoshi, Kosch Michael J., Makela Jonathan J., Takahashi Hisao

PROGRESS IN EARTH AND PLANETARY SCIENCE Vol. 2 2015.2

Daytime tweek atmospherics Reviewed

Ohya Hiroyo, Shiokawa Kazuo, Miyoshi Yoshizumi

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 120 ( 1 ) page： 654-665 2015.1

A statistical study of satellite traces and evolution of equatorial spread F Reviewed Open Access

Narayanan Viswanathan Lakshmi, Sau Sukanta, Gurubaran Subramanian, Shiokawa Kazuo, Balan Nanan, Emperumal Kaliappan, Sripathi Samireddipalle

EARTH PLANETS AND SPACE Vol. 66 2014.12

CME front and severe space weather Reviewed Open Access

N. Balan, R. Skoug, S. Tulasi Ram, P. K. Rajesh, K. Shiokawa, Y. Otsuka, I. S. Batista, Y. Ebihara, T. Nakamura

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 119 ( 12 ) page： 10,041 - 10,058 2014.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Thanks to the work of a number of scientists who made it known that severe space weather can cause extensive social and economic disruptions in the modern high-technology society. It is therefore important to understand what determines the severity of space weather and whether it can be predicted. We present results obtained from the analysis of coronal mass ejections (CMEs), solar energetic particle (SEP) events, interplanetary magnetic field (IMF), CME-magnetosphere coupling, and geomagnetic storms associated with the major space weather events since 1998 by combining data from the ACE and GOES satellites with geomagnetic parameters and the Carrington event of 1859, the Quebec event of 1989, and an event in 1958. The results seem to indicate that (1) it is the impulsive energy mainly due to the impulsive velocity and orientation of IMF B-z at the leading edge of the CMEs (or CME front) that determine the severity of space weather. (2) CMEs having high impulsive velocity (sudden nonfluctuating increase by over 275 km s(-1) over the background) caused severe space weather (SvSW) in the heliosphere (failure of the solar wind ion mode of Solar Wind Electron Proton Alpha Monitor in ACE) probably by suddenly accelerating the high-energy particles in the SEPs ahead directly or through the shocks. (3) The impact of such CMEs which also show the IMF B-z southward from the leading edge caused SvSW at the Earth including extreme geomagnetic storms of mean Dst(MP) < -250 nT during main phases, and the known electric power outages happened during some of these SvSW events. (4) The higher the impulsive velocity, the more severe the space weather, like faster weather fronts and tsunami fronts causing more severe damage through impulsive action. (5) The CMEs having IMF B-z northward at the leading edge do not seem to cause SvSW on Earth, although, later when the IMF B-z turns southward, they can lead to super geomagnetic storms of intensity (Dst(min)) less than even -400 nT.

DOI： 10.1002/2014JA020151

Airglow observations of nighttime medium-scale traveling ionospheric disturbances from Yonaguni: Statistical characteristics and low-latitude limit Reviewed

V. Lakshmi Narayanan, K. Shiokawa, Y. Otsuka, S. Saito

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 119 ( 11 ) page： 9268 - 9282 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

The characteristics of nighttime medium-scale traveling ionospheric disturbance (MSTID) features observed over Yonaguni (24.5 degrees N, 123.0 degrees E; 19.3 degrees N dip latitude), Japan are studied using all-sky imaging of OI 630.0nm airglow emission. The uniqueness of these observations is that the area observed by the imager covers the transition region between low to middle latitudes in the ionosphere. Typical low-latitude limit of midlatitude-type nighttime MSTIDs possessing phase front alignments along the northwest to the southeast occurs in this region. These MSTID features are rarely sighted at dip latitudes below 15 degrees. We selected 2 year period for analysis in which 1 year corresponded to the solar minimum conditions and another year to the solar maximum conditions. The MSTIDs were observed to extend to farther lower latitudes during the solar minimum conditions than during the solar maximum periods. Their observed range of wavelengths, phase velocities, phase front alignment, and propagation directions are similar to those observed at typical midlatitude sites. However, on many occasions the phase fronts of the observed MSTIDs did not extend over the whole field of view of the imager indicating that some process inhibits their extension to further lower latitudes. Detailed investigation suggests that the poleward propagating enhancement of airglow intensity, probably associated with the midnight pressure bulge, causes the MSTID features to disappear when they reach lower latitudes later in the night. When the MSTIDs reach lower latitudes well before midnight, they are found to be inhibited by the equatorial ionization anomaly crest region.

DOI： 10.1002/2014JA020368

Traveling planetary wave activity from mesopause region airglow temperatures determined by the Network for the Detection of Mesospheric Change (NDMC) Reviewed Open Access

E. R. Reisin, J. Scheer, M. E. Dyrland, F. Sigernes, C. S. Deehr, C. Schmidt, K. Hoeppner, M. Bittner, P. P. Ammosov, G. A. Gavrilyeva, J. Stegman, V. I. Perminov, A. I. Semenov, P. Knieling, R. Koppmann, K. Shiokawa, R. P. Lowe, M. J. Lopez-Gonzalez, E. Rodriguez, Y. Zhao, M. J. Taylor, R. A. Buriti, P. J. Espy, W. J. R. French, K. -U. Eichmann, J. P. Burrows, C. von Savigny

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 119 page： 71 - 82 2014.11

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

The global distribution of traveling planetary wave (PW) activity in the mesopause region is estimated for the first time from ground-based airglow measurements. Monthly and total mean climatologies of PW power are determined from rotational temperatures measured at 19 sites from 78 degrees N to 76 degrees S which contribute to the Network for the Detection of Mesospheric Change (NDMC). Wave power is expressed as the standard deviation of nocturnal mean temperature around the seasonal temperature variation. The results from 20 degrees N confirm the SABER traveling PW proxy by Offermann et al. (2009, J. Geophys. Res. 114, D06110) at two altitudes. Most sites between 69 degrees S and 69 degrees N show total mean traveling PW activity of about 6 K, and only some high latitude sites have considerably higher activity levels. At the two tropical sites, there is practically no seasonal variation of PW activity. At 70% of the midlatitude sites, the seasonal variation is moderate for most of the year, but it is quite appreciable at all high latitude sites. Results about traveling PW activity at 87 km and 95 km available from several sites signal similar behavior at both altitudes. The total mean climatological results here obtained have further been used to separate the traveling PW contribution from the superposition of wave types contained in OH rotational temperature fluctuations measured by the SCIAMACHY instrument on Envisat. A narrow equatorial wave activity maximum is probably caused by gravity waves, while a tendency towards greater activity at higher northern latitudes may be due to stationary planetary waves. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jastp.2014.07.002

Auroral Physics in the Earth's Magnetosphere Reviewed

SHIOKAWA Kazuo

Vol. 90 ( 11 ) page： 708-712 2014.11

Study of Pc1 pearl structures observed at multi-point ground stations in Russia, Japan, and Canada Reviewed Open Access

Jun Chae-Woo, Shiokawa Kazuo, Connors Martin, Schofield Ian, Poddelsky Igor, Shevtsov Boris

EARTH PLANETS AND SPACE Vol. 66 2014.10

Auroral fragmentation into patches Reviewed

Shiokawa Kazuo, Hashimoto Ayumi, Hori Tomoaki, Sakaguchi Kaori, Ogawa Yasunobu, Donovan Eric, Spanswick Emma, Connors Martin, Otsuka Yuichi, Oyama Shin-Ichiro, Nozawa Satonori, McWilliams Kathryn

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 119 ( 10 ) page： 8249-8261 2014.10

3D imaging reveals electrodynamics of polar cap aurora Reviewed

Dahlgren Hanna, Perry Gareth, St Maurice Jean-Pierre, Sundberg Torbjorn, Hosokawa Keisuke, Semeter Joshua L., Nicolls Michael J., Shiokawa Kazuo

ASTRONOMY & GEOPHYSICS Vol. 55 ( 5 ) page： . 2014.10

P130 広域多地点大気光観測による中間圏大気重力波(ポスター・セッション) Reviewed Open Access

鈴木臣, 塩川和夫, 大塚雄一, 川村誠治, 村山泰啓

大会講演予講集 Vol. 106 page： 212 2014.9

Ground-based ELF/VLF chorus observations at subauroral latitudes-VLF-CHAIN Campaign Reviewed

Shiokawa Kazuo, Yokoyama Yu, Ieda Akimasa, Miyoshi Yoshizumi, Nomura Reiko, Lee Sungeun, Sunagawa Naoki, Miyashita Yukinaga, Ozaki Mitsunori, Ishizaka Kazumasa, Yagitani Satoshi, Kataoka Ryuho, Tsuchiya Fuminori, Schofield Ian, Connors Martin

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 119 ( 9 ) 2014.9

New statistical analysis of the horizontal phase velocity distribution of gravity waves observed by airglow imaging Reviewed Open Access

Takashi S. Matsuda, Takuji Nakamura, Mitsumu K. Ejiri, Masaki Tsutsumi, Kazuo Shiokawa

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 119 ( 16 ) page： 9707 - 9718 2014.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We have developed a new analysis method for obtaining the power spectrum in the horizontal phase velocity domain from airglow intensity image data to study atmospheric gravity waves. This method can deal with extensive amounts of imaging data obtained on different years and at various observation sites without bias caused by different event extraction criteria for the person processing the data. The new method was applied to sodium airglow data obtained in 2011 at Syowa Station (69 degrees S, 40 degrees E), Antarctica. The results were compared with those obtained from a conventional event analysis in which the phase fronts were traced manually in order to estimate horizontal characteristics, such as wavelengths, phase velocities, and wave periods. The horizontal phase velocity of each wave event in the airglow images corresponded closely to a peak in the spectrum. The statistical results of spectral analysis showed an eastward offset of the horizontal phase velocity distribution. This could be interpreted as the existence of wave sources around the stratospheric eastward jet. Similar zonal anisotropy was also seen in the horizontal phase velocity distribution of the gravity waves by the event analysis. Both methods produce similar statistical results about directionality of atmospheric gravity waves. Galactic contamination of the spectrum was examined by calculating the apparent velocity of the stars and found to be limited for phase speeds lower than 30m/s. In conclusion, our new method is suitable for deriving the horizontal phase velocity characteristics of atmospheric gravity waves from an extensive amount of imaging data.

DOI： 10.1002/2014JD021543

Diagnostics of equatorial and low latitude ionosphere by TEC mapping over Brazil Reviewed

H. Takahashi, S. Costa, Y. Otsuka, K. Shiokawa, J. F. G. Monico, E. Paula, P. Nogueira, C. M. Denardini, F. Becker-Guedes, C. M. Wrasse, A. S. Ivo, V. C. F. Gomes, W. Gargarela, N. Sant'Anna, R. Gatto

ADVANCES IN SPACE RESEARCH Vol. 54 ( 3 ) page： 385 - 394 2014.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

The total electron content (TEC) in the equatorial and low-latitude ionosphere over Brazil was monitored in two dimensions by using 2011 data from the ground-based global navigation satellite system (GNSS) receiver network operated by the Brazilian Institute for Geography and Statistics. It was possible to monitor the spatial and temporal variations in TEC over Brazil continuously during both day and night with a temporal interval of 10 mm and a spatial resolution of about 400 km. The daytime equatorial ionization anomaly (ETA) and post-sunset plasma enhancement (PS-ETA) were monitored over an area corresponding to a longitudinal extension of 4000 km in South America. Considerable day-to-day variation was observed in ETA and PS-ETA. A large latitudinal and longitudinal gradient of TEC indicated a significant ionospheric range error in application of the GNSS positioning system. Large-scale plasma bubbles after sunset were also mapped over a wide range. Depletions with longitudinally separated by more than 800 km were observed. They were extended by more than 2000 km along the magnetic field lines and drifted eastward. It is expected that 2-dimensional TEC mapping can serve as a useful tool for diagnosing ionospheric weather, such as temporal and spatial variation in the equatorial plasma trough and crest, and particularly for monitoring the dynamics of plasma bubbles. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.asr.2014.01.032

Day-night coupling by a localized flow channel visualized by polar cap patch propagation Reviewed Open Access

Y. Nishimura, L. R. Lyons, Y. Zou, K. Oksavik, J. I. Moen, L. B. Clausen, E. F. Donovan, V. Angelopoulos, K. Shiokawa, J. M. Ruohoniemi, N. Nishitani, K. A. McWilliams, M. Lester

GEOPHYSICAL RESEARCH LETTERS Vol. 41 ( 11 ) page： 3701 - 3709 2014.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We present unique coordinated observations of the dayside auroral oval, polar cap, and nightside auroral oval by three all-sky imagers, two Super Dual Auroral Radar Network (SuperDARN) radars, and Defense Meteorological Satellite Program (DMSP)-17. This data set revealed that a dayside poleward moving auroral form (PMAF) evolved into a polar cap airglow patch that propagated across the polar cap and then nightside poleward boundary intensifications (PBIs). SuperDARN observations detected fast antisunward flows associated with the PMAF, and the DMSP satellite, whose conjunction occurred within a few minutes after the PMAF initiation, measured enhanced low-latitude boundary layer precipitation and enhanced plasma density with a strong antisunward flow burst. The polar cap patch was spatially and temporally coincident with a localized antisunward flow channel. The propagation across the polar cap and the subsequent PBIs suggests that the flow channel originated from dayside reconnection and then reached the nightside open-closed boundary, triggering localized nightside reconnection and flow bursts within the plasma sheet.

DOI： 10.1002/2014GL060301

Height-dependent ionospheric variations in the vicinity of nightside poleward expanding aurora after substorm onset Reviewed Open Access

S. Oyama, Y. Miyoshi, K. Shiokawa, J. Kurihara, T. T. Tsuda, B. J. Watkins

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 119 ( 5 ) page： 4146 - 4156 2014.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

High-latitude ionospheric variations at times near auroral substorms exhibit large temporal variations in both vertical and horizontal extents. Statistical analysis was made of data from the European Incoherent Scatter UHF radar at TromsO, Norway, and International Monitor for Auroral Geomagnetic Effects magnetometer for finding common features in electron density, ion and electron temperatures and relating these to currents and associated heating. This paper particularly focused on the height dependencies. Results show clear evidences of large electric field with corresponding frictional heating and Pedersen currents located just outside the front of the poleward expanding aurora, which typically appeared at the eastside of westward traveling surge. At the beginning of the substorm recovery phase, the ionospheric density had a large peak in the E region and a smaller peak in the F region. This structure was named as C form in this paper based on its shape in the altitude-time plot. The lower altitude density maximum is associated with hard auroral electron precipitation probably during pulsating aurora. We attribute the upper F region density maximum to local ionization by lower energy particle precipitation and/or long-lived plasma that is convected horizontally into the overhead measurement volume from the dayside hemisphere.

DOI： 10.1002/2013JA019704

Pi2 pulsation simultaneously observed in the E and F region ionosphere with the SuperDARN Hokkaido radar Reviewed Open Access

M. Teramoto, N. Nishitani, V. Pilipenko, T. Ogawa, K. Shiokawa, T. Nagatsuma, A. Yoshikawa, D. Baishev, K. T. Murata

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 119 ( 5 ) page： 3444 - 3462 2014.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We investigated Pi2 pulsations in the nightside ionosphere that began at 14:15 UT (2315 LT) on 11 July 2010, and they were observed with high-temporal (8s) resolution by beam 4 of the Super Dual Auroral Radar Network (SuperDARN) Hokkaido radar. These pulsations were simultaneously observed in both the ground/sea scatter echoes reflected from the F region height and in ionospheric echoes from field-aligned irregularities in the sporadic Es region. They had the same period of 110s and approximately no phase lag. From the radar observations and the International Geomagnetic Reference Field model, the amplitude of the eastward (EEW) component of the electric field of the Pi2 pulsations in the ionosphere was estimated similar to 8.0mV/m in the F region and similar to 2.0mV/m in the E region. Corresponding Pi2 pulsations appeared dominantly in the horizontal northward magnetic field component (H) at nearby ground stations, Moshiri (MSR), St. Paratunka (PTK), and Stecolny (STC), with amplitudes ranging from 6 nT (MSR) to 10 nT (STC). At the dominant frequency of 8.8 mHz, the coherences between H and EEW were high (>0.9), the cross phases of EEW relative to H were -56 degrees and -45 degrees, and the amplitude ratios were 2.7x105m/s and 8.4x105m/s, in the E and F regions, respectively. Based on a comparison of these results with theoretical predictions, we suggest that the concept of a pure cavity mode is not sufficient to explain the combined observations for midlatitude Pi2 waves and that the contribution of an Alfven waves must be taken in account.

DOI： 10.1002/2012JA018585

Global imaging of polar cap patches with dual airglow imagers Reviewed Open Access

K. Hosokawa, S. Taguchi, K. Shiokawa, Y. Otsuka, Y. Ogawa, M. Nicolls

GEOPHYSICAL RESEARCH LETTERS Vol. 41 ( 1 ) page： 1 - 6 2014.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

During a 2 h interval from 2240 to 2440 UT on 12 November 2012, regions of increased 630.0 nm airglow emissions were simultaneously detected by dual all-sky imagers in the polar cap, one at Longyearbyen, Norway (78.1 degrees N, 15.5 degrees E) and the other at Resolute Bay, Canada (74.7 degrees N, 265.1 degrees E). The Resolute Bay incoherent scatter radar observed clear enhancements of the F region electron density up to 10(12) m(-3) within these airglow structures which indicates that these are optical manifestations of polar cap patches propagating across the polar cap. During this interval of simultaneous airglow imaging, the nightside/dawnside (dayside/duskside) half of the patches was captured by the imager at Longyearbyen (Resolute Bay). This unique situation enabled us to estimate the dawn-dusk extent of the patches to be around 1500 km, which was at least 60-70% of the width of the antisunward plasma stream seen in the Super Dual Auroral Radar Network convection maps. In contrast to the large extent in the dawn-dusk direction, the noon-midnight thickness of each patch was less than 500 km. These observations demonstrate that there exists a class of patches showing cigar-shaped structures. Such patches could be produced in a wide range of local time on the dayside nearly simultaneously and spread across many hours of local time soon after their generation.

DOI： 10.1002/2013GL058748

Deducing Locations and Electrical properties of Lightning Discharges by ELF Network Observations in Japan Reviewed

Yasuhide Hobara, Masashi Hayaka, Kazuo Shiokawa

2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS) page： . 2014

Latitudinal variation of stochastic properties of the geomagnetic field Reviewed Open Access

Wanliss J. A., Shiokawa K., Yumoto K.

NONLINEAR PROCESSES IN GEOPHYSICS Vol. 21 ( 2 ) page： 347-356 2014

Ground-Based Observations of Hiss-Like Emissions Changed from Chorus Emissions and Related Pulsating Aurora Reviewed

Ozaki M., Sawai K., Yagitani S., Shiokawa K., Miyoshi Y., Kataoka R., Ieda A., Ebihara Y., Katoh Y.

2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS) 2014

Deducing locations and charge moment changes of lightning discharges by ELF network observations in Japan Reviewed Open Access

Hobara Y., Inoue T., Hayakawa M., Shiokawa K.

International Conference on Atmospheric Electricity Icae 2014 2014

Language：English Publishing type：Research paper (scientific journal) Publisher：International Conference on Atmospheric Electricity Icae 2014

Recent observations of electromagnetic radiations from lightning in the ELF frequency range so-called ELF transients are recognized as a powerful tool not only to deduce the global lightning distribution but also to obtain one of the most important properties of lightning discharges such as charge moment changes (CMCs). In this paper we demonstrate the spatio-temporal distributions of lightning discharges together with CMCs around Japan by using our newly developed domestic ELF observation network. This is the first time to obtain such type of distribution by using only ELF observations in the spatial scale of Japan (a few thousands km). We found that the obtained lightning source distributions both over the Pacific Ocean and the Sea of Japan are originated from the thunderstorm active regions confirmed by other measurements such as WWLLN. Statistical properties of the charge moment changes indicate that both number and CMC of positive CGs are superior to those of negative CGs. Moreover, considerably large CMC with both polarities are identified for the CGs over the Pacific Ocean as well as those with positive polarity over the Sea of Japan. Furthermore, we are going to present updated our lightning measurement network in Japan.

DOI： 10.1541/ieejpes.133.994

Deducing Locations and Charge Moment Changes of Lightning Discharges by ELF Network Observations in Japan Open Access

Hobara Yasuhide, Inoue Takahiro, Hayakawa Masashi, Shiokawa Kazuo

IEEJ Transactions on Power and Energy Vol. 133 ( 12 ) page： 994 - 1000 2013.12

Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electrical Engineers of Japan

The electromagnetic radiations from lightning discharges have been intensively studied for a long time in different frequency ranges. Recent observations of electromagnetic radiations from lightning in the ELF (extremely low frequency) frequency range so-called ELF transients are recognized as a powerful tool to obtain one of the most important properties of lightning discharges; the charge moment changes (Qds). In this paper we demonstrate the spatio-temporal distributions of lightning discharges together with their charge moment change (CMC) around Japan by using our newly developed domestic ELF observation network. This is the first time to obtain such type of distribution by using only ELF observations in the spatial scale of Japan (a few thousands km). We found that the obtained lightning source distributions both over the Pacific Ocean and the Sea of Japan are originated from the thunderstorm active regions confirmed by other measurements such as WWLLN. Statistical properties of the charge moment changes indicate that both number and CMC of positive CGs are superior to those of negative CGs. Moreover considerably large CMC with both polarities are identified for the CGs over the Pacific Ocean as well as those with positive polarity over the Sea of Japan.

DOI： 10.1541/ieejpes.133.994

イオノゾンデおよびファブリ・ペロー干渉計によって観測された子午面熱圏風の比較 Reviewed Open Access

Nishioka Michi, Maruyama Takashi, Otsuka Yuichi, Tsugawa Takuya, Ishibashi Hiromitsu, Shiokawa Kazuo, Ishii Mamoru

Antarctic record Vol. 57 ( 3 ) page： 357 - 368 2013.11

Language：English Publishing type：Research paper (scientific journal) Publisher：National Institute of Polar Research

電離圏ダイナミクスに大きく寄与する熱圏風についての理解を深めるため,イオノゾンデの磁気共役点観測により推定された南北方向の熱圏風(推定熱圏風)と,ファブリ・ペロー干渉計(FPI)観測により直接測定された南北方向の熱圏風との相関を調べた.推定熱圏風は,磁気共役点における熱圏風は等しい(赤道横断風モードが卓越する)という仮定のもとで導出される.2 つの手法で観測された夜間の熱圏風を比較するのは本研究が初めてである.2010 年のチェンマイ(タイ)とコトタバン(インドネシア)のイオノゾンデとFPI データを比較した結果,両者はおおむね良い相関を示したが,相関が悪い日もあった.相関が悪い事例は,赤道から収束・発散する成分を無視できず,赤道横断風モードが卓越するという仮定が成立しないと解釈されるものである.また,2 つの手法で求めた熱圏風の相関を季節別に調べると,2-4 月に両者の相関が高い一方,5-7 月に両者の相関が低いことがわかった.

DOI： 10.15094/00009710

Typhoon-induced concentric airglow structures in the mesopause region Reviewed

S. Suzuki, S. L. Vadas, K. Shiokawa, Y. Otsuka, S. Kawamura, Y. Murayama

GEOPHYSICAL RESEARCH LETTERS Vol. 40 ( 22 ) page： 5983 - 5987 2013.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We present the first reported gravity wave patterns in the mesopause region caused by a typhoon in the troposphere. On 10 December 2002, concentric rings of gravity waves in OH airglow were observed simultaneously by all-sky imagers in the Optical Mesosphere and Thermosphere Imager system in Japan, located at Rikubetsu (43.5 degrees N, 143.8 degrees E), Shigaraki (34.9 degrees N, 136.1 degrees E), and Sata (31.0 degrees N, 130.7 degrees E). The airglow structures, which were well defined and formed a coherent wave pattern expanding concentrically, were identified over 8 h (2135-2947 LT). We estimate the horizontal wavelength, horizontal phase speed, and wave period as 34.5 km, 50.2 m s(-1), and 11.5 min, respectively. Infrared cloud images from the Geostationary Meteorological Satellite show that the center of the rings estimated from the airglow data corresponds to a spiral band of Typhoon Pongsona (T0226). This unique event provides new insight into coupling between the lower and upper atmosphere.

DOI： 10.1002/2013GL058087

Comparison of meridional thermospheric winds observed by ionosondes and Fabry-Perot interferometers Reviewed Open Access

Nishioka M., Maruyama T., Otsuka Y., Tsugawa T., Ishibashi H., Shiokawa K., Ishii M.

Antarctic Record Vol. 57 ( 3 ) page： 357 - 368 2013.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Antarctic Record

To comprehend ionospheric-thermospheric coupling, one must understand the thermospheric wind system. However, measuring the thermospheric wind using a Fabry-Perot interferometer (FPI) is not an easy task. Because of this difficulty, some researchers have estimated meridional wind velocities using data obtained from a pair of ionosonde stations near the geomagnetic conjugate points, under the assumption that the meridional wind is the same at the two ionosonde stations (transequatorial mode wind). In this paper, we construct the first comparison of the estimated meridional wind velocities with meridional wind observed with FPIs. We analyzed data from the ionosondes and FPIs installed at Chiang Mai, Thailand, and Kototabang, Indonesia, from 2010. We found that the estimated and observed wind velocities were generally in good agreement on most nights, although on some nights, the wind velocities were different. The assumption that the meridional wind is equal anywhere between the two ionosonde stations would not be suitable for the days when the winds were not in good agreement. We also investigated the seasonal dependence of the correlation between the estimated and observed meridional winds. They were in good agreement from February to April and were not in good agreement from May to July. © 2013 National Institute of Polar Research.

DOI： 10.15094/00009710

Planetary wave induced wind and airglow oscillations in the middle latitude MLT region Reviewed

Recent advances in equatorial, low- and mid-latitude aeronomy Preface Reviewed

Archana Bhattacharyya, Jorge L. Chau, Clezio M. Denardini, David L. Hysell, Jonathan J. Makela, Kazuo Shiokawa, Erhan Kudeki

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 103 page： 1 - 2 2013.10

Observation of nighttime medium-scale travelling ionospheric disturbances by two 630-nm airglow imagers near the auroral zone Reviewed

Shiokawa K., Mori M., Otsuka Y., Oyama S., Nozawa S., Suzuki S., Connors M.

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 103 page： 184-194 2013.9

Ionogram-based range-time displays for observing relationships between ionosonde satellite traces, spread F and drifting optical plasma depletions Reviewed

Lynn K. J. W., Otsuka Y., Shiokawa K.

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 98 page： 105-112 2013.6

H. Takahashi, K. Shiokawa, F. Egito, Y. Murayama, S. Kawamura, C. M. Wrasse

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 98 page： 97 - 104 2013.6

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Upper mesosphere airglow emissions and temperature observed at Rikubetsu (43.5 degrees N,143.8 degrees E) and mesospheric winds observed at Wakkanai (45.4 degrees N,141.8 degrees E), Japan, from January to December 2005 were used to analyze periodic oscillations of 2-16 days. During the January to March period and after September, both winds and airglow demonstrated clear 8-, 10- and 16-day oscillations. Downward phase progressions observed in the oscillations indicate that these are a signature of Rossby mode planetary waves. The 16-day wave was more evident in the zonal wind than the meridional. The 10-day wave was observed in January and March, on the basis of only a few cycles superposed on the 16-day wave. Airglow OI 557.7 nm, O-2 and OH(6,2) band emissions and O-2 rotational temperature also showed significant amplitude of oscillation induced by the wave passages. For the 10-day wave, OI557.7 nm showed an amplitude of oscillation equals to or more than 50% of the mean intensity level, O-2 similar to 45% and OH 25%. Large amplitudes of oscillation of the airglow during the passage of planetary waves suggest the possible vertical transport of atomic oxygen in addition to the density and temperature variations intrinsic to the wave events. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jastp.2013.03.014

プラズマバブル発生に伴う全電子数変化率の緯度依存性

Substorm onset and expansion phase intensification precursors seen in polar cap patches and arcs Reviewed

Nishimura Y., Lyons L. R., Shiokawa K., Angelopoulos V., Donovan E. F., Mende S. B.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 118 ( 5 ) page： 2034 - 2042 2013.5

鈴木順也, 中田裕之, 鷹野敏明, 津川卓也, 斉藤昭則, 大塚雄一, 塩川和夫

大気電気学会誌 = / Society of Atmospheric Electricity of Japan Vol. 7 ( 1 ) page： 60 - 61 2013.4

Evidence of gravity wave ducting in the mesopause region from airglow network observations Reviewed Open Access

Suzuki, S, Shiokawa, K, Otsuka, Y, Kawamura, S, Murayama, Y

GEOPHYSICAL RESEARCH LETTERS Vol. 40 ( 3 ) page： 601 - 605 2013.2

Ground and satellite observations of low-latitude red auroras at the initial phase of magnetic storms Reviewed Open Access

K. Shiokawa, Y. Miyoshi, P. C. Brandt, D. S. Evans, H. U. Frey, J. Goldstein, K. Yumoto

Journal of Geophysical Research: Space Physics Vol. 118 ( 1 ) page： 256 - 270 2013.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

We report ground and satellite observations of unique low-latitude red auroras that appear at the initial phase of geomagnetic storms. For two events on 21 October 2001, and 6 April 2000, the low-latitude red auroras appeared at ∼45° MLAT (L ∼ 2) ∼ 1.5 h after the storm sudden commencement in the postmidnight sector in Japan. Comprehensive satellite data were available for the former event. The energetic neutral atom images obtained by the Imager for Magnetopause-to-Aurora Global Exploration satellite show rapid enhancement of ring current hydrogen and oxygen fluxes at radial distances of ∼ 2-8 RE after the storm sudden commencement and associated with several storm-time substorms. The hydrogen ring-current enhancement occurred particularly in the postmidnight sector where the red aurora was observed. The timing of oxygen flux enhancement associated with a storm-time substorm coincided with the red aurora appearance. This rapid and significant enhancement of energetic neutral atom flux was also confirmed by energetic ion data obtained by the NOAA/POES-16 satellite. Extreme ultraviolet plasmaspheric images obtained by Magnetopause-to-Aurora Global Exploration indicate that the plasmapause was located at L = 2.3-2.5 in the postmidnight sector during the event, indicating that a spatial overlap occurs between the plasmasphere and the enhanced ring current ions at L ∼ 2. Based on these observations, we suggest that large energization of high-energy ring-current ions in the postmidnight inner magnetosphere caused the spatial overlap of these ring-current ions with the low-energy plasmaspheric plasmas at L ∼ 2, producing the low-latitude red auroras at the very beginning of the storms. ©2012. American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JA018001

Geomagnetic conjugate observations of plasma-sheet electrons by the FAST and THEMIS satellites Reviewed Open Access

S. Lee, K. Shiokawa, J. P. McFadden, K. Seki

Journal of Geophysical Research: Space Physics Vol. 118 ( 1 ) page： 132 - 145 2013.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

We investigate pitch-angle distributions and spectral shapes of auroral electrons simultaneously observed during three conjunction events by the FAST satellite at altitudes of 2500-3500 km and by the THEMIS satellite in the plasma sheet at 7-13 RE. All three events were on the lower latitude of the auroral oval. Conjunction event 1 occurred at ~1914:45 UT on 10 April 2008. Electron spectra at energies of 0.1-3 keV are correlated well between the two satellites, while the precipitating electrons above 3 keV are missing at FAST. Event 2 occurred at 1255:26 UT on 26 April 2008. Electron spectra above 3 keV are correlated well between the two satellites. An additional broad spectral peak at energies of 0.1-0.5 keV was observed by FAST. Event 3 occurred at 0058:04 UT on 25 December 2008. Precipitating electrons of 0.5-5 keV obtained by FAST are correlated well with those of THEMIS-C, while a monoenergetic peak at 0.1-0.2 keV was observed only by FAST. For the three conjunction events, we conclude that high-energy precipitating auroral electrons observed by FAST directly come from the equatorial plasma sheet, while low-energy precipitating electrons may come from middle altitudes as a result of acceleration by static potential differences. For missing high-energy (&gt
3 keV) electrons of event 1, we speculate that the pitch-angle scattering by waves occurs only at a limited energy range. ©2012. American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JA017805

GPS observations of medium-scale traveling ionospheric disturbances over Europe Reviewed Open Access

Otsuka, Y, Suzuki, K, Nakagawa, S, Nishioka, M, Shiokawa, K, Tsugawa, T

ANNALES GEOPHYSICAE Vol. 31 ( 2 ) page： 163 - 172 2013

Stereoscopic determination of all-sky altitude map of aurora using two ground-based Nikon DSLR cameras Reviewed Open Access

R. Kataoka, Y. Miyoshi, K. Shigematsu, D. Hampton, Y. Mori, T. Kubo, A. Yamashita, M. Tanaka, T. Takahei, T. Nakai, H. Miyahara, K. Shiokawa

ANNALES GEOPHYSICAE Vol. 31 ( 9 ) page： 1543 - 1548 2013

Language：English Publishing type：Research paper (scientific journal) Publisher：COPERNICUS GESELLSCHAFT MBH

A new stereoscopic measurement technique is developed to obtain an all-sky altitude map of aurora using two ground-based digital single-lens reflex (DSLR) cameras. Two identical full-color all-sky cameras were set with an 8 km separation across the Chatanika area in Alaska (Poker Flat Research Range and Aurora Borealis Lodge) to find localized emission height with the maximum correlation of the apparent patterns in the localized pixels applying a method of the geographical coordinate transform. It is found that a typical ray structure of discrete aurora shows the broad altitude distribution above 100 km, while a typical patchy structure of pulsating aurora shows the narrow altitude distribution of less than 100 km. Because of its portability and low cost of the DSLR camera systems, the new technique may open a unique opportunity not only for scientists but also for night-sky photographers to complementarily attend the aurora science to potentially form a dense observation network.

DOI： 10.5194/angeo-31-1543-2013

Special Issue: Recent Progress in the Vertical Coupling in the Atmosphere-Ionosphere System Preface Reviewed

Drift velocities of 150-km field-aligned irregularities observed by the equatorial atmosphere radar Reviewed Open Access

Otsuka Y, Mizutani N, Shiokawa K, Patra A, Yokoyama T, Yamamoto M

Antarctic Record Vol. 57 ( 3 ) page： 369 - 378 2013

Giant ionospheric disturbances observed with the SuperDARN Hokkaido HF radar and GPS network after the 2011 Tohoku earthquake Reviewed Open Access

Ogawa Tadahiko, Nishitani Nozomu, Tsugawa Takuya, Shiokawa Kazuo

EARTH PLANETS AND SPACE Vol. 64 ( 12 ) page： 1295-1307 2012.12

Dora Pancheva, Kazuo Shiokawa, Petra Knizova, Weixing Wan

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 90-91 ( 1 ) page： V - VI 2012.12

Development of low-cost sky-scanning Fabry-Perot interferometers for airglow and auroral studies Reviewed Open Access

K. Shiokawa, Y. Otsuka, S. Oyama, S. Nozawa, M. Satoh, Y. Katoh, Y. Hamaguchi, Y. Yamamoto, J. Meriwether

EARTH PLANETS AND SPACE Vol. 64 ( 11 ) page： 1033 - 1046 2012.11

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：TERRA SCIENTIFIC PUBL CO

We have developed new Fabry-Perot interferometers (FPIs) that are designed to measure thermospheric winds and temperatures as well as mesospheric winds through the airglow/aurora emissions at wavelengths of 630.0 nm and 557.7 nm, respectively. One FPI (FP01), possessing a large aperture etalon (diameter: 116 mm), was installed at the EISCAT Tromso site in 2009. The other FPIs, using 70-mm diameter etalons, were installed in Thailand, Indonesia, and Australia in 2010-2011 (FP02-FP04) by the Solar-Terrestrial Environment Laboratory, and in Peru (Nazca and Jicamarca) and Alaska (Poker Flat) by Clemson University. The FPIs with 70-mm etalons are low-cost compact instruments, suitable for multipoint network observations. All of these FPIs use low-noise cooled-CCD detectors with 1024 x 1024 pixels combined with a 4-stage thermoelectric cooling system that can cool the CCD temperature down to -80 degrees C. The large incident angle (maximum: 1.3 degrees-1.4 degrees) to the etalon achieved by the use of multiple orders increases the throughput of the FPIs. The airglow and aurora observations at Tromso by FP01 show wind velocities with typical random errors ranging from 2 to 13 m s(-1) and from 4 to 27 m s(-1) for mesosphere (557.7 nm) and thermosphere (630.0 nm) measurements, respectively. The 630.0-nm airglow observations at Shigaraki, Japan, by FP02-FP04 and by the American FPI instruments give thermospheric wind velocities with typical random errors that vary from 2 m s(-1) to more than 50 m s(-1) depending on airglow intensity.

DOI： 10.5047/eps.2012.05.004

Reflection height of daytime tweek atmospherics during the solar eclipse of 22 July 2009 Reviewed Open Access

Hiroyo Ohya, Fuminori Tsuchiya, Hiroyuki Nakata, Kazuo Shiokawa, Yoshizumi Miyoshi, Kozo Yamashita, Yukihiro Takahashi

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 11 ) 2012.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report multipoint observations of daytime tweek atmospherics during the solar eclipse of 22 July 2009. Sixteen and sixty-three tweek atmospherics were observed at Moshiri and Kagoshima, Japan, where the magnitudes of the solar eclipse were 0.458 and 0.966, respectively. This was the first observation of tweek atmospherics during a low-magnitude eclipse (0.458). The average and standard deviation of the reflection height were 94.9 +/- 13.7 km at Moshiri and 87.2 +/- 12.9 km at Kagoshima. The reflection height at Moshiri was almost the same as that for normal nighttime conditions in July (96.7 +/- 12.6 km) in spite of the low magnitude of the eclipse. The reflection height at Kagoshima seems be divided into two parts: propagation across the total solar eclipse path and propagation in the partial solar eclipse path. During the eclipse, we also observed the phase variation in the LF transmitter signals. The average change in the phase delay of the LF signals was 109 degrees for the paths that crossed the eclipse path and 27 degrees for the paths that did not cross the eclipse path. Assuming a normal daytime height for LF waves of 65 km, a ray tracing analysis indicates that the variations in phase correspond to a height increase of 5-6 km for the paths across the eclipse and 1-2 km for partial eclipse paths. The wide range of estimated tweek reflection heights at Kagoshima also suggests a difference in electron density in the lower ionosphere between total and partial solar eclipses.

DOI： 10.1029/2012JA018151

Observation of equatorial nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow images over 7 years Reviewed Open Access

D. Fukushima, K. Shiokawa, Y. Otsuka, T. Ogawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 10 ) 2012.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report on nighttime medium- scale traveling ionospheric disturbances (MSTIDs) observed at Kototabang, Indonesia (geographic longitude: 100.3 degrees E; geographic latitude: 0.2 degrees S; and geomagnetic latitude: 10.6 degrees S) during a 7-year period from October 2002 to October 2009. MSTIDs were observed in 630-nm nighttime airglow images by using a highly sensitive all-sky airglow imager at Kototabang. The averages and standard deviations of horizontal phase velocity, period, and horizontal wavelength of MSTIDs observed during the 7 years were 320 +/- 170 m/s, 42 +/- 11 min, and 790 +/- 440 km, respectively. The occurrence rate of the observed MSTIDs decreased with decreasing solar activity. The average horizontal wavelength of MSTIDs increased with decreasing solar activity. Southward MSTIDs were dominant throughout the 7 years of observations. These facts are consistent with the hypothesis that the observed MSTIDs are caused by gravity waves in the thermosphere. Moreover, we compared the propagation directions of the observed MSTIDs with the locations of tropospheric convection activity for the events where gravity waves producing the observed MSTIDs could have existed in the lower atmosphere. Strong tropospheric convection was found within +/- 30 degrees from the source directions of MSTIDs in 81% of the MSTID events. In such events, gravity waves were possibly generated from deep convection in the troposphere and directly propagated into the thermosphere.

DOI： 10.1029/2012JA017758

Motion of high-latitude nighttime medium-scale traveling ionospheric disturbances associated with auroral brightening Reviewed Open Access

Shiokawa, K, Mori, M, Otsuka, Y, Oyama, S, Nozawa, S

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 10 ) 2012.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report for the first time the rapid oscillating motion of nighttime medium-scale traveling ionospheric disturbances (MSTIDs) based on airglow imaging observations at Tromso (magnetic latitude: 67.1 degrees N), Norway on 8 December, 2009. The MSTIDs appeared in 630-nm airglow images at 1530 UT as wave-like structures south of Tromso with a horizontal wavelength of similar to 200 km and a phase surface of north to south. They moved eastward with velocities of 30-60 m/s. The velocity was faster in the poleward-side of the MSTIDs, forming a northeast-southwest phase surface at later times. This phase surface direction is opposite to that of midlatitude MSTIDs. The MSTIDs show sudden oscillations and phase jump in the east-west direction with a timescale of similar to 10 min at 1730 UT. The oscillations were associated with an auroral brightening observed at the poleward edge of the images and small magnetic field perturbations observed by ground magnetometers. The Doppler measurement of the 630-nm airglow by a Fabry-Perot interferometer at Tromso showed a stable southeastward thermospheric wind with a velocity of similar to 150 m/s. These observations indicate that the MSTID oscillations were linked to auroral electric field in the ionosphere, implying that the observed MSTIDs are ionospheric plasma structures. We suggest that the observed MSTIDs were created by atmospheric gravity waves at the beginning, left as fossil plasma structures even after the gravity wave packet dissipated in the thermosphere, moved eastward according to the background electric field driven by the F-region dynamo, and oscillated associated with the auroral electric field.

DOI： 10.1029/2012JA017928

Magnetospheric responses to the passage of the interplanetary shock on 24 November 2008 Reviewed

K-H Kim, D-H Lee, K. Shiokawa, E. Lee, J-S Park, H-J Kwon, V. Angelopoulos, Y-D. Park, J. Hwang, N. Nishitani, T. Hori, K. Koga, T. Obara, K. Yumoto, D. G. Baishev

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 10 ) 2012.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

The passage of an interplanetary (IP) shock was detected by Wind, ACE, Geotail, and THEMIS-B in the solar wind on 24 November 2008. From the propagation time of the IP shock at the spacecraft, it is expected that the IP shock front is aligned with the Parker spiral and strikes the postnoon dayside magnetopause first. Using multipoint observations of the sudden commencement (SC) at THEMIS probes, GOES 11, and ETS in the dayside magnetosphere, we confirmed that the magnetospheric response to the IP shock starts earlier in the postnoon sector than in the prenoon sector. We found that the estimated normal direction of the SC front is nearly aligned with the estimated IP shock normal. We also found that the SC front normal speed is much slower than the fast mode speed and is about 22-56% of the IP shock speed traveling in the solar wind. Thus, we suggest that the major field changes of the SC in the dayside magnetosphere are not due to the magnetic flux carried by hydromagnetic waves but to the increased solar wind dynamic pressure behind the shock front sweeping the magnetopause. The SC event appears as a step-like increase in the H component at the low-latitude Bohyun station and a negative-then-positive variation in the H component at the high-latitude Chokurdakh (CHD) station in the morning sector. During the negative perturbation at CHD, the SuperDARN Hokkaido radar detected a downward motion in the ionosphere, implying westward electric field enhancement. Using the THEMIS electric field data, it is confirmed that the westward electric field corresponds to the inward plasma motion in the dayside magnetosphere due to the magnetospheric compression.

DOI： 10.1029/2012JA017871

Visualization of ion cyclotron wave and particle interactions in the inner magnetosphere via THEMIS-ASI observations Reviewed Open Access

K. Sakaguchi, Y. Miyoshi, E. Spanswick, E. Donovan, I. R. Mann, V. Jordanova, K. Shiokawa, M. Connors, J. C. Green

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 10 ) 2012.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Interaction with EMIC (electromagnetic ion cyclotron) waves is thought to be a key component contributing to the very rapid loss of both ring current and radiation belt particles into the atmosphere. Estimated loss rates are heavily dependent on the assumed spatial distribution of the EMIC wave. Statistical maps of the spatial distribution have been produced using in-situ satellite data. However, with limited satellite data it is impossible to deduce the true spatial distribution. In this study, we present ground-based observations using all-sky imager and search coil magnetometer networks, which provide the large-scale distribution and motion of the EMIC wave-particle interaction regions. We observed several spots of isolated proton auroras simultaneously with Pc1/EMIC waves at subauroral latitudes during the expansion phase of a storm-time substorm on 9 March 2008. The isolated auroras were distributed over similar to 4-hours MLT preceding midnight. The POES-17 satellite confirmed enhancements of 30-keV proton precipitations over the isolated auroras. The equatorward motion of the auroras and frequency drift of the wave were consistent with the plasmasphere eroding due to a polar cap potential enhancement modeled by a numerical simulation. We also found that relativistic electron precipitation was not always associated with the isolated aurora, depending strongly on the plasma density profile near the plasmapause. This study shows that the specific distribution of ring current proton precipitation can be visualized through the ground network observations. By combining with upcoming inner-magnetosphere satellite missions, these remote-sensing observations are very important for quantitative understanding of the particle loss in the inner magnetosphere.

DOI： 10.1029/2012JA018180

Space-time variability of polar cap patches: Direct evidence for internal plasma structuring Reviewed Open Access

Dahlgren H., Perry G. W., Semeter J. L., St-Maurice J. -P., Hosokawa K., Nicolls M. J., Greffen M., Shiokawa K., Heinselman C.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 9 ) 2012.9

Observed correlation between pulsating aurora and chorus waves at Syowa Station in Antarctica: a case study Reviewed Open Access

Ozaki, M, S. Yagitani, K. Ishizaka, K. Shiokawa, Y. Miyoshi, A. Kadokura, H. Yamagishi, R. Kataoka, A. Ieda, Y. Ebihara, N. Sato, I. Nagano

J. Geophys. Res. Vol. 117 ( A8 ) page： 8211 - 8211 2012.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

A high correlation between a pulsating auroral patch and grouped chorus waves was observed on 17 April 2006 at Syowa Station in Antarctica. The spatial distribution of aurora-chorus correlation coefficients is evaluated in order to determine the source region. A pulsating patch at the highest-correlation pixel shows a one-to-one correspondence with the intensity variation of the grouped chorus waves, consisting of successive rising-tone elements with a duration and spacing of 2-3 s and 20-30 s, respectively. The generation region of the chorus waves is estimated from the latitude and longitude dependence of the equatorial electron gyrofrequencies using the IGRF geomagnetic field model. The extent of the estimated latitude and longitude is consistent with the spatial distribution of the high-correlation aurora-chorus region. The time difference between the chorus waves and the scattered electrons is also evaluated to discuss the validity of the source region. It shows that electrons reached the ionosphere sooner than the associated chorus waves by similar to 1 s, consistent with the theoretical value for conjugate pulsating aurora generated at the equator. These results support the hypothesis that pulsating aurora is caused by pitch angle scattering of high-energy electrons by whistler mode chorus waves, via a cyclotron resonance at the equator. These results are the first ground-based observations of high correlations between a spatially extended aurora and chorus waves.

DOI： 10.1029/2011JA017478

On post-midnight field-aligned irregularities observed with a 30.8-MHz radar at a low latitude: Comparison with F-layer altitude near the geomagnetic equator Reviewed

M. Nishioka, Y. Otsuka, K. Shiokawa, T. Tsugawa, Effendy, P. Supnithi, T. Nagatsuma, K. T. Murata

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 8 ) 2012.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We investigated the relationship between post-midnight F-region field aligned irregularities (FAIs) and F-layer altitude by analyzing data of a 30.8-MHz radar installed 5at Kototabang, Indonesia (0.2 degrees S, 100.3 degrees E; geomagnetic latitude 10.4 degrees S) and an ionosonde installed at Chumphon, Thailand (10.7 degrees N, 99.4 degrees E; geomagnetic latitude 3.3 degrees N). Chumphon is located near the geomagnetic equator on approximately the same meridian as Kototabang. Case studies show that the altitude of the F-layer rose at Chumphon a half hour before the post-midnight FAIs appeared at Kototabang. The Doppler velocity of the E-region FAIs observed simultaneously by the 30.8-MHz radar was downward, indicating that the F-layer uplift was not caused by the electric field. We also investigated seasonal variations of the post-midnight FAI occurrence and the F-layer altitude. Both the post-midnight FAIs and the uplift of the F-layer were frequently seen around midnight between May and August. The seasonal variation of the midnight F-layer uplift around the geomagnetic equator coincided with that of the post-midnight FAI occurrence at Kototabang. These results suggest that the uplift of the F-layer would play an important role in the generation of post-midnight FAIs. We evaluated the linear growth rate of the Rayleigh-Taylor instability based on the altitude of the F-layer observed at Chumphon. The result shows that the uplift of the F-layer can enhance the growth rate because gravity-driven eastward electric current increases. Therefore, we interpret that the observed FAIs were accompanied by plasma bubble, the growth rate of which was reinforced by the uplifted F-layer.

DOI： 10.1029/2012JA017692

Disappearance of equatorial plasma bubble after interaction with mid-latitude medium-scale traveling ionospheric disturbance Reviewed Open Access

Otsuka, Y, Shiokawa, K, Ogawa, T

GEOPHYSICAL RESEARCH LETTERS Vol. 39 ( 14 ) 2012.7

GPS total electron content variations associated with poleward moving Sun-aligned arcs Reviewed Open Access

Jayachandran P. T., Hosokawa K., Shiokawa K., Otsuka Y., Watson C., Mushini S. C., MacDougall J. W., Prikryl P., Chadwick R., Kelly T. D.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 5 ) 2012.5

Direct three-dimensional imaging of polar ionospheric structures with the Resolute Bay Incoherent Scatter Radar Reviewed Open Access

H. Dahlgren, J. L. Semeter, K. Hosokawa, M. J. Nicolls, T. W. Butler, M. G. Johnsen, K. Shiokawa, C. Heinselman

GEOPHYSICAL RESEARCH LETTERS Vol. 39 ( 5 ) 2012.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Ionospheric plasma density structures in the dayside F-region of the polar cap are commonly occurring events, but adequate measurements of their formation and evolution have been sparse. With the advent of the advanced modular incoherent scatter radar RISR-N (Resolute Bay Incoherent Scatter Radar) it is now possible for the first time to study the temporal evolution of the plasma properties in the polar cap region in three dimensions, with a spatial resolution of tens of kilometers, from which the plasma rest frame can be experimentally established. We demonstrate the strength of the diagnostic with observations from an event of enhanced plasma density observed over Resolute Bay in December 2009. A colocated all-sky imager showed faint 630.0 and 557.7 nm emission corresponding to the plasma enhancements, and the structures could be traced back to a formation region in the open/closed field line boundary. This new plasma imaging technique will provide important information on the mechanisms controlling the structuring in the high latitude ionosphere. Citation: Dahlgren, H., J. L. Semeter, K. Hosokawa, M. J. Nicolls, T. W. Butler, M. G. Johnsen, K. Shiokawa, and C. Heinselman (2012), Direct three-dimensional imaging of polar ionospheric structures with the Resolute Bay Incoherent Scatter Radar, Geophys. Res. Lett., 39, L05104, doi:10.1029/2012GL050895.

DOI： 10.1029/2012GL050895

Electron and wave characteristics observed by the THEMIS satellites near the magnetic equator during a pulsating aurora Reviewed

A. Nakajima, K. Shiokawa, K. Sakaguchi, Y. Miyoshi, S. Lee, V. Angelopoulos, O. Le Contel, J. P. McFadden, J. W. Bonnell, K. -H. Fornacon, E. Donovan

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 2012.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Based on conjugate ground and THEMIS satellite observations, we show electron spectra and wave characteristics near the magnetic equatorial plane during a pulsating aurora event on the high latitude side of the auroral oval. The pulsating aurora was observed by a 30-Hz sampled all-sky imager (ASI) at Gillam (56.4 degrees N, 265.4 degrees E), Canada, at similar to 0840-0910 UT on 8 January 2008. The auroral intensity pulsation at the possible THEMIS D (THD) footprints had frequency peaks at similar to 0.1-0.2 Hz. The footprint of THD was in the poleward part of the proton aurora observed by a meridian-scanning photometer. After auroral pulsation began at similar to 0842 UT, both THD and THEMIS E which was near THD in the mid-tail at 11.6-11.8 R-E, observed enhanced field-aligned electron fluxes at energies of 1-10 keV. However, the amplitudes of whistler mode waves and electrostatic cyclotron harmonics (ECH) waves observed by THD with the highest sampling rate of 8 kHz were not significant, showing a marked contrast to the recent report of clear correlation between whistler mode waves and auroral pulsations observed at 5-9 R-E. We suggest that the observed field-aligned electrons, which are probably caused by Fermi-type acceleration associated with earthward plasma flow in the mid-tail plasma sheet, are modulated by some wave processes to cause pulsating auroras.

DOI： 10.1029/2011JA017066

Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes Reviewed Open Access

Nomura R., Shiokawa K., Sakaguchi K., Otsuka Y., Connors M.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 2 ) 2012.2

Signatures of moving polar cap arcs in the F-region PolarDARN echoes Reviewed Open Access

A. V. Koustov, K. Hosokawa, N. Nishitani, K. Shiokawa, H. Liu

ANNALES GEOPHYSICAE Vol. 30 ( 3 ) page： 441 - 455 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：COPERNICUS GESELLSCHAFT MBH

Joint observations of the all-sky camera at Resolute Bay (Nunavut, Canada) and the Polar Dual Auroral Radar Network (PolarDARN) HF radars at Rankin Inlet and Inuvik (Canada) are considered to establish radar signatures of poleward moving polar cap arcs 'detaching' from the auroral oval. Common features of the events considered are enhanced power or echo occurrence in the wake of the arcs and enhanced spectral width of these echoes. When the arcs were oriented along some of the radar beams, velocity reversals at the arc location were observed with the directions of the arc-associated flows corresponding to a converging electric field. For the event of 9 December 2007, two arcs were poleward progressing almost along the central beams of the Inuvik radar at the speed close to the E x B drift of the bulk of the F-region plasma as inferred from HF Doppler velocities and from independent measurements by the Resolute Bay ionosonde. In global-scale convection maps inferred from all Super Dual Auroral Radar Network (SuperDARN) radar measurements, the polar cap arcs were often seen close to the reversal line of additional mesoscale convection cells located poleward of the normal cells related to the auroral oval.

DOI： 10.5194/angeo-30-441-2012

The Energization and Radiation in Geospace (ERG) Project Reviewed

Y. Miyoshi, T. Ono, T. Takashima, K. Asamura, M. Hirahara, Y. Kasaba, A. Matsuoka, H. Kojima, K. Shiokawa, K. Seki, M. Fujimoto, T. Nagatsuma, C. Z. Cheng, Y. Kazama, S. Kasahara, T. Mitani, H. Matsumoto, N. Higashio, A. Kumamoto, S. Yagitani, Y. Kasahara, K. Ishisaka, L. Blomberg, A. Fujimoto, Y. Katoh, Y. Ebihara, Y. Omura, M. Nose, T. Hori, Y. Miyashita, Y. -M. Tanaka, T. Segawa

DYNAMICS OF THE EARTH'S RADIATION BELTS AND INNER MAGNETOSPHERE Vol. 199 page： 103 - 116 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER GEOPHYSICAL UNION

The Energization and Radiation in Geospace (ERG) project for solar cycle 24 will explore how relativistic electrons in the radiation belts are generated during space stout's. This geospace exploration project consists of three research teams: the ERG satellite observation team, the ground-based network observation team, and the integrated data analysis/simulation team. Satellite observation will provide in situ measurements of features such as the plasma distribution function, electric and magnetic fields, and plasma waves, whereas remote sensing by ground-based observations using, for example, HF radars, magnetometers, optical instruments, and radio wave receivers will provide the global state of the geospace. Various kinds of data will be integrated and compared with numerical simulations for quantitative understanding. Such a synergetic approach is essential for comprehensive understanding of relativistic electron generation/loss processes through cross-energy and cross-regional coupling in which different plasma populations and regions are dynamically coupled with each other. In addition, the ERG satellite will utilize a new and innovative measurement technique for wave-particle interactions that can directly measure the energy exchange process between particles and plasma waves. In this paper, we briefly review some of the profound problems regarding relativistic electron accelerations and losses that will be solved by the ERG project, and we provide an overview of the project.

DOI： 10.1029/2012GM001304

Auroral Signatures of the Dynamic Plasma Sheet Reviewed Open Access

A. Keiling, K. Shiokawa, V. Uritsky, V. Sergeev, E. Zesta, L. Kepko, N. Ostgaard

AURORAL PHENOMENOLOGY AND MAGNETOSPHERIC PROCESSES: EARTH AND OTHER PLANETS Vol. 197 page： 317 - + 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER GEOPHYSICAL UNION

Understanding the physical connections of the coupled magnetosphere-ionosphere system will result in a more complete explanation of the aurora and will further the goal of being able to interpret the global auroral distributions as a dynamic map of the magnetosphere. Significant advances have been made in recent years toward this goal. In this chapter, we briefly review, while focusing on recent observations, selected auroral phenomena that are driven by magnetospheric processes. These include expansion of substorm aurora, plasma sheet waves and auroral modulations, ballooning instability and auroral beads, dipolarization/plasma injections and the auroral bulge, poleward boundary intensifications and auroral streamers, vortical flows and auroral spirals, and plasma flows prior to auroral onset. In addition, other auroral phenomena, such as auroral arcs, diffuse auroras, auroral asymmetry/conjugacy in the conjugate hemispheres, and auroral magneto spheric currents, are highlighted here but expanded in other chapters of this monograph for in-depth reviews.

DOI： 10.1029/2012GM001231

VHF radar observations of post-midnight f-region field-aligned irregularities over indonesia during solar minimum Reviewed

Y. Otsuka, K. Shiokawa, M. Nishioka, Effendy

Indian Journal of Radio and Space Physics Vol. 41 ( 2 ) page： 199 - 207 2012

Language：English Publishing type：Research paper (scientific journal)

A VHF backscatter radar with operating frequency 30.8 MHz has been operated at Kototabang (0.20°S, 100.32°E
dip latitude 10.4°S), Indonesia since February 2006. The F-region field-aligned irregularities (FAIs) observed by this radar from February 2006 to December 2010 during a solar minimum period have been analyzed and found that FAIs appeared frequently at the post-midnight sector between May and August every year from 2006 to 2010. Five-beam measurements by the radar revealed zonal propagation of the F-region FAIs. The present paper reports, for the first time, statistics of the zonal propagation velocity of the post-midnight FAIs. Between May and August, 46% (14%) of the post-midnight FAIs propagated westward (eastward), and zonal propagation was not discernible for 40% of the post-midnight FAIs. Average velocity was approximately 50 m s-1 westward. The post-midnight FAIs were likely associated with either plasma bubbles or medium-scale traveling ionospheric disturbances (MSTIDs).

High-latitude GPS TEC changes associated with a sudden magnetospheric compression Reviewed Open Access

P. T. Jayachandran, C. Watson, I. J. Rae, J. W. MacDougall, D. W. Danskin, R. Chadwick, T. D. Kelly, P. Prikryl, K. Meziane, K. Shiokawa

GEOPHYSICAL RESEARCH LETTERS Vol. 38 ( 23 ) 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Using ionospheric total electron content (TEC) measured by Global Positioning System (GPS) receivers of the Canadian High Arctic Ionospheric Network (CHAIN) we provide clear evidence for a systematic and propagating temporary TEC enhancement produced by compression of the magnetosphere due to a sudden increase in solar wind dynamic pressure. The magnetospheric compression is evident in THEMIS/GOES satellite data. Application of a GPS triangulation technique revealed that the TEC changes propagated with a speed of 3-6 km/s in the antisunward direction near noon and similar to 8 km/s in the sunward direction in the pre-noon lower latitude sector. Characteristics of these TEC changes along with riometer absorption measurements seems to indicate that the TEC change is due to electron density enhancement in the F region and is possibly due to particle precipitation associated with sudden magnetospheric compression. Citation: Jayachandran, P. T., C. Watson, I. J. Rae, J. W. MacDougall, D. W. Danskin, R. Chadwick, T. D. Kelly, P. Prikryl, K. Meziane, and K. Shiokawa (2011), Highlatitude GPS TEC changes associated with a sudden magnetospheric compression, Geophys. Res. Lett., 38, L23104, doi: 10.1029/2011GL050041.

DOI： 10.1029/2011GL050041

Simultaneous observations at Darwin of equatorial bubbles by ionosonde-based range/time displays and airglow imaging Reviewed Open Access

K. J. W. Lynn, Y. Otsuka, K. Shiokawa

GEOPHYSICAL RESEARCH LETTERS Vol. 38 ( 23 ) 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Airglow observations of ionospheric electron density depletions made at Darwin, Australia have demonstrated that the tree-like structure of bubbles developed at the magnetic equator are mapped along magnetic field lines with considerable accuracy to the base of the ionosphere at higher latitudes. Ionosonde range-time displays made at Darwin and other equatorial sites in the Australian region show characteristic approaching and receding echoes which converge on a typical spread-F event. These off-angle echoes have often been referred to in the literature as satellite traces and associated with spread F with little recognition of their true significance. All four optical depletions previously reported in the literature as being seen at Darwin are found in this paper to be accompanied by such typical off-angle/spread F events. The zonal drift velocity of the moving reflectors can be measured from the speed at which such echoes approach and recede. Since digital ionosondes in equatorial sites have existed for many years, existing ionogram data, when suitably processed into range-time displays, may allow the occurrence of such events over several sunspot cycles to be found. A question remains as to whether all or only some of such equatorial range-time events correspond to electron density depletions. Citation: Lynn, K. J. W., Y. Otsuka, and K. Shiokawa (2011), Simultaneous observations at Darwin of equatorial bubbles by ionosonde-based range/time displays and airglow imaging, Geophys. Res. Lett., 38, L23101, doi:10.1029/2011GL049856.

DOI： 10.1029/2011GL049856

A statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) Reviewed Open Access

Lee S., Shiokawa K., McFadden J. P., Nishimura Y.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 116 2011.12

Long-term variations in tweek reflection height in the D and lower E regions of the ionosphere Reviewed Open Access

Hiroyo Ohya, Kazuo Shiokawa, Yoshizumi Miyoshi

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 116 ( 10 ) 2011.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We investigated, for the first time, long-term (1976-2010) variations in reflection heights of tweek atmospherics based on very low frequency (VLF) observations at Kagoshima, Japan. The results revealed the effects of the solar cycle on the nighttime lower ionosphere at low to middle latitudes. The tweek reflection heights on geomagnetically quiet days were analyzed every month over three solar cycles by using an automated spectral fitting procedure to estimate the cutoff frequency. The average and standard deviation of the reflection height were 95.9 km and +/-3.1 km, respectively. Typical periods of time variation for the reflection height were 13.3, 3.2, 1.3, 1.0, 0.6, and 0.5 years. The variations in tweek reflection heights did not show simple anticorrelation with solar activity. The correlation coefficient between tweek reflection height and sunspot number was 0.03 throughout the three solar cycles. Hilbert-Huang transform analysis successfully indicated the presence of 0.5-1.5 year and similar to 10 year variations as intrinsic mode functions (IMF). The decomposed IMF with the similar to 10 year variation had a positive correlation with sunspot numbers and a negative correlation with galactic cosmic rays (GCRs). We hypothesize that these variations in tweek reflection heights could be caused by coupling of several ionization effects at the D and lower E regions, effects such as geocorona, GCRs, particle precipitation, and variations in neutral density in the lower thermosphere. Among these processes, the geocorona and particle precipitation could show negative correlation, while the GCRs and neutral density could show positive correlation with solar activities.

DOI： 10.1029/2011JA016800

ジオスペース探査ERG計画(Technical Session,ICSANE 2011(International Conference on Space, Aeronautical and Navigational Electronics 2011))

小野高幸, 浅村和史, 三好由純, 高島健, 平原聖文, 小原隆博, 笠羽康正, 熊本篤志, 松岡彩子, 小嶋浩嗣, 塩川和夫, 関華奈子, 藤本正樹, 長妻努

電子情報通信学会技術研究報告. SANE, 宇宙・航行エレクトロニクス Vol. 111 ( 239 ) page： 57 - 61 2011.10

An empirical model of the quiet daily geomagnetic field variation Reviewed Open Access

Y. Yamazaki, K. Yumoto, M. G. Cardinal, B. J. Fraser, P. Hattori, Y. Kakinami, J. Y. Liu, K. J. W. Lynn, R. Marshall, D. McNamara, T. Nagatsuma, V. M. Nikiforov, R. E. Otadoy, M. Ruhimat, B. M. Shevtsov, K. Shiokawa, S. Abe, T. Uozumi, A. Yoshikawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 116 2011.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

An empirical model of the quiet daily geomagnetic field variation has been constructed based on geomagnetic data obtained from 21 stations along the 210 Magnetic Meridian of the Circum-pan Pacific Magnetometer Network (CPMN) from 1996 to 2007. Using the least squares fitting method for geomagnetically quiet days (Kp <= 2+), the quiet daily geomagnetic field variation at each station was described as a function of solar activity SA, day of year DOY, lunar age LA, and local time LT. After interpolation in latitude, the model can describe solar-activity dependence and seasonal dependence of solar quiet daily variations (S) and lunar quiet daily variations (L). We performed a spherical harmonic analysis (SHA) on these S and L variations to examine average characteristics of the equivalent external current systems. We found three particularly noteworthy results. First, the total current intensity of the S current system is largely controlled by solar activity while its focus position is not significantly affected by solar activity. Second, we found that seasonal variations of the S current intensity exhibit north-south asymmetry; the current intensity of the northern vortex shows a prominent annual variation while the southern vortex shows a clear semi-annual variation as well as annual variation. Thirdly, we found that the total intensity of the L current system changes depending on solar activity and season; seasonal variations of the L current intensity show an enhancement during the December solstice, independent of the level of solar activity.

DOI： 10.1029/2011JA016487

Ground-based multispectral high-speed imaging of flickering aurora Reviewed Open Access

Ryuho Kataoka, Yoshizumi Miyoshi, Takeshi Sakanoi, Ayumi Yaegashi, Yusuke Ebihara, Kazuo Shiokawa

GEOPHYSICAL RESEARCH LETTERS Vol. 38 ( 14 ) 2011.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

It has been suggested that dispersive Alfven waves (DAWs) are capable of accelerating electrons via Landau resonance, and the interference of DAWs plays an essential role to create flickering auroral patterns. Here we show evidence that the leading front of a typical interference pattern is more energetic than the trailing part, based on ground-based high-speed imaging observations at wavelengths of 670.5 nm and 844.6 nm, which are sensitive to relatively hard and soft electrons, respectively. The fine spatial resolution of 9.5 deg field-of-view at magnetic zenith and the 100 Hz sampling rate of electron multiplying charge-coupled device (EMCCD) enabled us to resolve the spatiotemporal variation of the flickering aurora. It is found that there is only 10 ms time delay with 0.5 km spatial shift on average in the obtained flickering patterns at two wavelengths. The time delay and spatial shift can be comprehensively explained by the traveling inhomogeneous interference pattern of DAWs, probably associated with the Landau damping and/or time-of-flight effect, which is only detectable using the highest resolved temporal and spatial observations of flickering aurora. Citation: Kataoka, R., Y. Miyoshi, T. Sakanoi, A. Yaegashi, Y. Ebihara, and K. Shiokawa (2011), Ground-based multispectral high-speed imaging of flickering aurora, Geophys. Res. Lett., 38, L14106, doi:10.1029/2011GL048317.

DOI： 10.1029/2011GL048317

Decay of polar cap patch Reviewed Open Access

K. Hosokawa, J. I. Moen, K. Shiokawa, Y. Otsuka

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 116 ( 5 ) 2011.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report an event in which a polar cap patch was detected with an all-sky imager (ASI) at Resolute Bay, Canada (74.73 degrees N, 265.07 degrees E; AACGM latitude 82.9 degrees), on the nightside. The patch stopped its antisunward motion associated with a northward turning of interplanetary magnetic field and stayed within the field of view of the ASI for more than 1 h. When the patch stagnated, its luminosity decreased gradually, which allows us to investigate how the patch plasma decayed in a quantitative manner. The decay of the patch can be quantitatively explained by the loss through recombinations of O(+) with ambient N(2) and O(2) molecules, if we assume the altitude of the optical patch to be around 295 km. The derived altitude of the patch around 295 km is much higher than the nominal value at 235 km obtained from the MSIS-E90 and IRI-2007 models, indicating that climatological models such as IRI are not suitable for describing the actual density profile of patches. This is probably because the loss process was much faster in the lower-altitude part of the patch; thus, the peak altitude of the patch increased as it traveled across the polar cap because of rapid recombination at the bottomside of the F region. This suggests that we should employ higher emission altitude when we investigate optical patches transported deep into the nightside polar cap. Such information is important when we compare the optical data with other instruments such as coherent radars and GPS scintillation measurements by mapping the all-sky image on the geographic coordinate system with an assumption of the patch emission altitude.

DOI： 10.1029/2010JA016297

Turbulent microstructures and formation of folds in auroral breakup arc Reviewed Open Access

Ryuho Kataoka, Yoshizumi Miyoshi, Takeshi Sakanoi, Ayumi Yaegashi, Kazuo Shiokawa, Yusuke Ebihara

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 116 ( 4 ) 2011.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We conducted a ground-based optical measurement pointing at local magnetic zenith with a narrow field of view of 9.3 degrees by 9.3 degrees, using a high-speed electron multiplier charge-coupled device camera at Poker Flat Research Range. We show evidence that auroral folds were periodically formed in a breakup arc and the luminosity is exponentially increased for about 10 s before an auroral breakup onset. The evolution of turbulent microstructures and the formation of folds may be interpreted by the nonlinear evolution of inertial Alfven wave (IAW) turbulence in the thin current sheet. On the basis of these optical observations, we discuss a possible role of the ionosphere for modulating the triggering process of the onset via the self-organization of the IAW turbulence associated with Kelvin-Helmholtz and tearing instabilities of the thin current sheet.

DOI： 10.1029/2010JA016334

GEONETにおけるプラズマバブルに伴う全電子数変化率とロック損失との相関 Reviewed

菊地隼人, 中田裕之, 津川卓也, 大塚雄一, 鷹野敏明, 島倉信, 塩川和夫, 小川忠彦

大気電気学会誌 = / Society of Atmospheric Electricity of Japan Vol. 5 ( 1 ) page： 82 - 83 2011.4

First satellite-imaging observation of medium-scale traveling ionospheric disturbances by FORMOSAT-2/ISUAL Reviewed

Toru Adachi, Yuichi Otsuka, Masashi Yamaoka, Mamoru Yamamoto, Kazuo Shiokawa, Alfred B. Chen, Rue-Ron Hsu

GEOPHYSICAL RESEARCH LETTERS Vol. 38 ( 4 ) 2011.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

On the night of May 16, 2007, a satellite limb imager of FORMOSAT-2/ISUAL observed wave-like structures of the 630-nm airglow simultaneously with an all-sky imager deployed at Darwin in Australia. The height of the airglow layer was estimated as 220 km, and the structures were aligned in the northeast-southwest orientation with a wavelength of similar to 300 km and propagated toward the northwest with a phase velocity of similar to 100 m s(-1), showing typical characteristics of the nighttime medium-scale traveling ionospheric disturbances (MSTIDs). We conclude that ISUAL for the first time succeeded in observing the airglow layer altitude and airglow structures modulated by MSTID from space. Such a satellite limb airglow imaging could be a new tool to characterize ionospheric irregularities on a global level. Citation: Adachi, T., Y. Otsuka, M. Yamaoka, M. Yamamoto, K. Shiokawa, A. B. Chen, and R.-R. Hsu (2011), First satellite-imaging observation of medium-scale traveling ionospheric disturbances by FORMOSAT-2/ISUAL, Geophys. Res. Lett., 38, L04101, doi:10.1029/2010GL046268.

DOI： 10.1029/2010GL046268

Periodic black auroral patches at the dawnside dipolarization front during a substorm Reviewed

K. Sakaguchi, K. Shiokawa, E. Donovan, A. Nakajima, Y. Hiraki, T. Trondsen, F. Plaschke

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 116 2011.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Periodic black auroral patches were observed in the Canadian postmidnight sector by ground-based all-sky cameras during an auroral substorm. The aurora consisted of several black patches of similar to 50 km (similar to 1 degrees in longitude) scales that appeared along the equatorward edges of the proton auroras over a 3 h local time segment from Gillam to Sanikiluaq ground stations 15 min after the auroral intensification occurred in Alaska. To the best of our knowledge, this type of black auroras has never been reported before, although the surrounding luminous auroras evolve into the well-known torch structures later. In situ observations by the THEMIS satellites, three of which were close to being magnetically conjugate in the plasma sheet, as well as ground-based proton auroral observations, show that a dipolarization front and associated dawnward ion flows propagated eastward at poleward of the black patches coinciding with their appearance. The flow motions of auroras observed poleward of the black patches are possibly generated by decelerations of dawnward ion flow because of the consistency of both durations and positions. We speculate, based on manifestations of high-pressure regions in dipolarized flux tubes, the pressure-driven interchange instability formed a beading shape (periodic black patches) of field-aligned currents. The black auroral patches developed into torch structures after the flow disappearance, indicating the dawnward flows might stabilize and limit the instability within a narrow L shell where the pressure gradient is directed Earthward and flows cannot enter. We conclude that the periodic black patches arise as a consequence of a relaxation process of enhanced plasma pressure near the inner boundary of the plasma sheet during a substorm.

DOI： 10.1029/2010JA015957

ULF impulsive magnetic response at mid-latitudes to lightning activity Reviewed Open Access

A. Schekotov, V. Pilipenko, K. Shiokawa, E. Fedorov

EARTH PLANETS AND SPACE Vol. 63 ( 2 ) page： 119 - 128 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER HEIDELBERG

Induction magnetometer data from the mid-latitude station Moshiri (geomagnetic latitude 35.6 degrees.) has been examined in search of a transient ULF response to the regional lightning activity. For many events, besides the main impulse produced by the lightning discharge, a secondary impulse delayed about 1 sec was observed. These secondary echo-impulses are probably caused by the partial reflection of wave energy of the initial lightning pulse from the upper boundary of the ionospheric Alfven resonator in the topside ionosphere. The modeling with artificial signals has shown that a multi-band spectral resonant structure (SRS) can be formed owing to the occurrence of paired pulses in analyzed time series. The statistical superposed epoch method indeed has revealed a dominance of two-pulse structure in the magnetic field background during the periods of the SRS occurrence.

DOI： 10.5047/eps.2010.12.009

Atmospheric wave induced O-2 and OH airglow intensity variations: effect of vertical wavelength and damping Reviewed Open Access

H. Takahashi, A. Onohara, K. Shiokawa, F. Vargas, D. Gobbi

ANNALES GEOPHYSICAE Vol. 29 ( 4 ) page： 631 - 637 2011

Frequency-dependent polarization characteristics of Pc1 geomagnetic pulsations observed by multipoint ground stations at low latitudes Reviewed Open Access

R. Nomura, K. Shiokawa, V. Pilipenko, B. Shevtsov

Journal of Geophysical Research: Space Physics Vol. 116 ( 1 ) 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

We have investigated Pc1 geomagnetic pulsations observed by induction magnetometers at three low-latitude stations (Paratunka (PTK), Moshiri (MSR), and Sata (STA), L=1.2-2.1). A detailed polarization analysis shows that polarization parameters (angle of polarization ellipse orientation, ψ, and polarization sense, ε) of individual Pc1 bands depend on frequency at all three stations. The dependence of ψ on frequency was seen in ∼70% of the 93 Pc1 events observed at MSR (L=1.5) from 14 July 2007 to 13 July 2009. The maxima of seasonal and diurnal variations of the occurrence rate were in winter and during the nighttime, as reported previously, indicating that the transmission of observed Pc1 pulsations to lower latitudes is controlled by the density of the F layer plasma. These facts suggest that spatially distributed Pc1 waves with varying frequencies depending on longitude or latitude at high latitudes propagated in the ionospheric duct to cause the frequency dependence of polarization parameters at low latitudes. We also suggest that the Pc1 pearl structure with a repetition period of ∼5-30 s observed at low latitudes is a beat of high-latitude waves with slightly different frequencies. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2010JA015684

プラズマバブルに伴う全電子数変化率・ロック損失分布 : ロック損失発生の有無と全電子数変化率の相関 Reviewed

Motion of polar cap arcs Reviewed Open Access

Hosokawa, K, J. I. Moen, K. Shiokawa, Y. Otsuka

Journal of Geophysical Research Vol. 116 ( 1 ) 2011

Statistical Study of Medium-Scale Traveling Ionospheric Disturbances Observed with a GPS Receiver Network in Japan Reviewed

Otsuka, Y, Kotake, N, Shiokawa, K, Ogawa, T, Tsugawa, T, Saito, A

AERONOMY OF THE EARTH'S ATMOSPHERE AND IONOSPHERE Vol. 2 page： 291 - 299 2011

Dynamic temporal evolution of polar cap tongue of ionization during magnetic storm Reviewed

Hosokawa K., Tsugawa T., Shiokawa K., Otsuka Y., Nishitani N., Ogawa T., Hairston M. R.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 115 2010.12

Simultaneous airglow, lidar, and radar measurements of mesospheric gravity waves over Japan Reviewed Open Access

Suzuki S., Nakamura T., Ejiri M. K., Tsutsumi M., Shiokawa K., Kawahara T. D.

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 115 2010.12

菊地隼人, 中田裕之, 津川卓也, 大塚雄一, 西岡未知, 鷹野敏明, 島倉信, 塩川和夫, 小川忠彦

大気電気学会誌 = / Society of Atmospheric Electricity of Japan Vol. 4 ( 2 ) page： 80 - 81 2010.10

Simultaneous FAST and Double Star TC1 observations of broadband electrons during a storm time substorm Reviewed Open Access

A. Nakajima, K. Shiokawa, K. Seki, R. Nakamura, K. Keika, W. Baumjohann, T. Takada, J. P. McFadden, C. W. Carlson, A. N. Fazakerley, H. Reme, I. Dandouras, R. J. Strangeway, O. Le Contel, N. Cornilleau-Wehrlin, K. H. Yearby

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 115 2010.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Broadband electrons (BBEs) exhibit remarkable electron flux enhancements over a broad energy range (0.03-30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. Here, we report a BBE event observed by the Fast Auroral Snapshot (FAST) satellite at 1355-1359 UT, similar to 61 degrees-66 degrees invariant latitudes, similar to 0600 magnetic local time (MLT), and similar to 3800 km altitude during a storm on 25 July 2004. The Double Star (DS) TC1 satellite was located near the magnetic equator at L = 5.7, close to the same local time as FAST. We investigate the acceleration process of BBEs from the inner magnetosphere to near the ionosphere by comparing electron data obtained by FAST and DS TC1. We also investigate both plasma and field variations in the inner magnetosphere associated with substorm onset using DS TC1 data to examine the relationship between the BBEs and the storm time substorm. Ground geomagnetic field data show a positive H-bay at similar to 1349 UT at similar to 0600 MLT, indicating that a storm time substorm started just before the appearance of the BBEs. At similar to 1350 UT, a tailward ion flow was observed by DS TC1. Then, DS TC1 observed a local dipolarization and a drastic ion density enhancement at similar to 1351 UT, indicating that particle heating associated with the substorm was occurring in the inner magnetosphere. From similar to 1352 UT, electron fluxes were isotropically enhanced at energies above similar to 0.5 keV as observed by DS TC1. On the other hand, the pitch angle distribution of BBEs at the FAST altitude showed field-aligned lower-energy electrons below similar to 0.5 keV and isotropic higher-energy electrons above similar to 0.5 keV. From these data, it was inferred that the BBEs might consist of two energy components due to the acceleration or heating of electrons at different altitudes in association with the storm time substorm.

DOI： 10.1029/2009JA014907

プラズマバブルに伴うGPSロック損失・全電子数変化率分布のマルチイベント解析 Reviewed

菊地隼人, 中田裕之, 津川卓也, 大塚雄一, 鷹野敏明, 島倉信, 塩川和夫, 小川忠彦

大気電気学会誌 = / Society of Atmospheric Electricity of Japan Vol. 4 ( 1 ) page： 58 - 59 2010.4

Rayleigh-Taylor type instability in auroral patches Reviewed

K. Shiokawa, A. Nakajima, A. Ieda, K. Sakaguchi, R. Nomura, T. Aslaksen, M. Greffen, E. Donovan

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 115 2010.2

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Based on observations by a high-resolution narrow field-of-view CCD camera, we found small-scale (5-25 km) finger-like structures at the western boundary of auroral patches in images obtained at Gillam (geomagnetic latitude: 65.5 degrees N), Canada, in January 2008. Since shear motion was not observed along the boundary of the patches, we suggest that these structures are formed by macroscopic Rayleigh-Taylor type plasma instability arising in the magnetospheric equatorial plane from the force balancing of the (eastward) magnetic tension force and the (westward) pressure gradient force.

DOI： 10.1029/2009JA014273

A physical mechanism of positive ionospheric storms at low latitudes and midlatitudes Reviewed Open Access

Balan N., Shiokawa K., Otsuka Y., Kikuchi T., Lekshmi D. Vijaya, Kawamura S., Yamamoto M., Bailey G. J.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 115 2010.2

Reorganization of polar cap patches through shears in the background plasma convection Reviewed

Hosokawa K., St-Maurice J. -P., Sofko G. J., Shiokawa K., Otsuka Y., Ogawa T.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 115 2010.1

The STEL induction magnetometer network for observation of high-frequency geomagnetic pulsations Reviewed Open Access

K. Shiokawa, R. Nomura, K. Sakaguchi, Y. Otsuka, Y. Hamaguchi, M. Satoh, Y. Katoh, Y. Yamamoto, B. M. Shevtsov, S. Smirnov, I. Poddelsky, M. Connors

EARTH PLANETS AND SPACE Vol. 62 ( 6 ) page： 517 - 524 2010

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER HEIDELBERG

The Solar-Terrestrial Environment Laboratory (STEL) induction magnetometer network has been developed to investigate the propagation characteristics of high-frequency geomagnetic pulsations in the Pc1 frequency range (0.2-5 Hz). Five induction magnetometers were installed in the period 2005-2008 at Athabasca in Canada, Magadan and Paratunka in Far East Russia, and Moshiri and Sata in Japan. The sensitivity of these magnetometers is between 0.3 and 13 V/nT at turnover frequencies of 1.7-5.5 Hz. GPS time pulses are used for accurate triggering of the 64-Hz data sampling. We show examples of PiB/Pc1 magnetic pulsations observed at these five stations, as well as the harmonic structure of ionospheric Alfven resonators observed at Moshiri. We found that the Pc1 packets are slightly modulated as they propagate from high to low latitudes in the ionospheric duct. These network observations are expected to contribute to our understanding of Pc1-range magnetic pulsations and their interaction with relativistic electrons by combining the obtained results with future satellite missions that observe radiation belt particles.

DOI： 10.5047/eps.2010.05.003

Erratum: Geospace Exploration Mission: ERG Project

MIYOSHI Yoshizumi, SEKI Kanako, SHIOKAWA Kazuo, ONO Takayuki, KASABA Yasumasa, KUMAMOTO Atsushi, HIRAHARA Masafumi, TAKASHIMA Takeshi, ASAMURA Kazushi, MATSUOKA Ayako, NAGATSUMA Tsutomu, Working Group ERG

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN Vol. 8 ( ists27 ) page： Tm_13 2010

Language：English Publishing type：Research paper (scientific journal) Publisher：THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES

This paper describes a small-satellite mission for geospace exploration ERG (Energization and Radiation in Geospace) that aims at understanding the acceleration process of relativistic electrons and dynamical variations of the space storm. The project consists of not only the satellite mission but also ground-based observations and integrated studies/simulation teams. The satellite will be launched into the inner magnetosphere around the next solar maximum. In efforts to understand the cross-energy coupling process that is essential to generate relativistic electrons and the dynamical evolution of space storms, the satellite is equipped with instruments for comprehensively observing plasma/particles, fields and waves. Possible international collaborations are also discussed in this paper.

DOI： 10.2322/tastj.8.tm_13

Geospace Exploration Mission: ERG Project Reviewed

MIYOSHI Yoshizumi, MATSUOKA Ayako, NAGATSUMA Tsutomu, Working Group ERG, SEKI Kanako, SHIOKAWA Kazuo, ONO Takayuki, KASABA Yasumasa, KUMAMOTO Atsushi, HIRAHARA Masafumi, TAKASHIMA Takeshi, ASAMURA Kazushi

TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN Vol. 8 ( 27 ) page： Tm_1-Tm_6 2010

Calculation of the parameter η krassovsky airglow emissions from the O2 (0-1) and OH (6-2) Reviewed Open Access

Amelia Naomi Onohara, Hisao Takahashi, Delano Gobbi, Kazuo Shiokawa

Revista Brasileira de Geofisica Vol. 28 ( 4 ) page： 579 - 592 2010

Language：Portuguese Publishing type：Research paper (scientific journal) Publisher：Sociedade Brasileira de Geofisica

In this work, the Krassovsky's η parameter, was used to investigate the amplitudes and phases of periodic variations of O2(0-1) and OH(6-2) airglow emissions. The data set was obtained from photometer measurements at Rikubetsu (43.5°N, 143.8°E), Japan, from March 2004 to August 2005, under collaboration with STEL-LAB (Solar-Terrestrial Environment Laboratory), Nagoya University. The results showed |η| = 5.3 ± 1.7 and Φ = -40.2°± 30.6° for O2 emission, and {pipe}η{pipe} = 8.0 ± 4.7 and Φ = -41.9°± 41.4° for OH emission. There is a good agreement between the results obtained in this work with the previous results. But, it must be emphasized that the models for Φ don't predict the results as good as the models for |η|. It was found the existence of larger |η| values for the OH emission, so that there are few results in literature concerning of this high values. Comparing it with the models of Schubert et al. (1991), it was observed that they have good correlation with the model for a gravity wave with a horizontal wavelength of 100 km. © 2010 Sociedade Brasileira de Geofísica.

DOI： 10.1590/S0102-261X2010000400004

Lower-thermospheric wind fluctuations measured with an FPI during pulsating aurora at Tromso, Norway Reviewed Open Access

S. Oyama, K. Shiokawa, J. Kurihara, T. T. Tsuda, S. Nozawa, Y. Ogawa, Y. Otsuka, B. J. Watkins

ANNALES GEOPHYSICAE Vol. 28 ( 10 ) page： 1847 - 1857 2010

Language：English Publishing type：Research paper (scientific journal) Publisher：COPERNICUS GESELLSCHAFT MBH

Simultaneous observations were conducted with a Fabry-Perot Interferometer (FPI) at a wavelength of 557.7 nm, an all-sky camera at a wavelength of 557.7 nm, and the European Incoherent Scatter (EISCAT) UHF radar during the Dynamics and Energetics of the Lower Thermosphere in Aurora 2 (DELTA-2) campaign in January 2009. This paper concentrated on two events during periods of pulsating aurora. The lower-thermospheric wind velocity measured with the FPI showed obvious fluctuations in both vertical and horizontal components. Of particular interest is that the location of the fluctuations was found in a darker area that appeared within the pulsating aurora. During the same time period, the EISCAT radar observed sporadic enhancements in the F-region backscatter echo power, which suggests the presence of low-energy electron (1 keV or lower) precipitation coinciding with increase in amplitude of the electromagnetic wave (at the order of 10 Hz or higher). While we have not yet identified the dominant mechanism causing the fluctuations in FPI-derived wind velocity during the pulsating aurora, the frictional heating energy dissipated by the electric-field perturbations may be responsible for the increase in ionospheric thermal energy thus modifying the local wind dynamics in the lower thermosphere.

DOI： 10.5194/angeo-28-1847-2010

Telescope of Extreme Ultraviolet boarded on KAGUYA: Science from the Moon Reviewed

Yoshikawa, I, Murakami, G, Ezawa, F, Yoshioka, K, Obana, Y, Taguchi, M, Yamazaki, A, Kameda, S, Nakamura, M, Kikuchi, M, Kagitani, M, Okano, S, Shiokawa, K, Miyake, W

Advances in Geosciences Vol. 19 page： 109 - 121 2010

Language：English Publishing type：Research paper (scientific journal)

We have succeeded in observations by the Telescope of Extreme Ultraviolet (TEX) aboard Japan's lunar orbiter KAGUYA to characterize the evolution of the Earth's plasmasphere. The view afforded by the KAGUYA orbit encompasses the plasma distribution in a single exposure, enabling us to examine for the first time the globally-averaged properties of the plasmasphere from the side (meridian) view. We focus on a study period that began with a likely moderate erosion event of plasma patches in a geomagnetically disturbed period, and follow refilling of plasma from the upper ionosphere. The Earth's plasmasphere grew up to saturated level at the rate of approximately 1,600 km per day to 4,800 km per day on the equatorial plane. From the “side view” of the Earth, a specific magnetic flux tube with cold dense plasmas was seen and likely moved to outer magnetosphere, even while geomagnetic activity was low. From the moon, we are studying the terrestrial plasmas in the vicinity of the Earth. This is called “Geoscience from the Moon”.

DOI： 10.1142/9789812838162_0009

Azimuthal structures of ray auroras at the beginning of auroral substorms Reviewed

K. Sakaguchi, K. Shiokawa, E. Donovan

GEOPHYSICAL RESEARCH LETTERS Vol. 36 ( 23 ) 2009.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

The time evolution of optical structures in brightening auroras was examined for two substorm events that occurred on January 15, 2008 and February 27, 2009. The onsets of both auroral substorms were captured in the field of view of an all-sky TV camera at Gillam, Canada. We found that in both cases, the brightening auroras formed vertical structures, or so-called 'ray auroras', which lined up longitudinally for several tens of seconds before luminosity increased sharply. The ray structure implies precipitating electrons accelerated over a broad energy range at substorm onset. Two dimensional Fourier transform analysis of the auroral images showed the ray auroras have characteristic wavenumbers and harmonics that develop within a few seconds of the initial brightening. These results suggest that dispersive Alfven waves containing turbulent parallel electric fields form in brightening regions at the beginning of auroral substorms. Citation: Sakaguchi, K., K. Shiokawa, and E. Donovan ( 2009), Azimuthal structures of ray auroras at the beginning of auroral substorms, Geophys. Res. Lett., 36, L23106, doi: 10.1029/2009GL041252.

DOI： 10.1029/2009GL041252

GPS total electron content variations associated with a polar cap arc Reviewed Open Access

P. T. Jayachandran, K. Hosokawa, J. W. MacDougall, S. Mushini, R. B. Langley, K. Shiokawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 114 ( 12 ) 2009.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report an example of total electron content (TEC) variations, using Global Positioning System (GPS) measurements, associated with a polar cap arc detected by an all-sky imager and ionosonde at a polar cap station. During the transit of the arc, GPS signals along the arc length showed an increase of similar to 2 TEC units whereas GPS signals perpendicular to the arc showed only an increase of similar to 0.3 TEC units. This indicates that the GPS TEC variations associated with a polar cap arc are dependent on the geometry of the GPS raypaths with respect to the arc. Ionosonde measurements confirm that this arc was an E region feature at similar to 110 km with peak electron density of 5.4 x 10(11) el/m(3). Estimated speed of the arc using a GPS triangulation method was about 300 m/s.

DOI： 10.1029/2009JA014916

Ionospheric and geomagnetic disturbances during the 2005 Sumatran earthquakes Reviewed

Alina Marie Hasbi, Mohammed Awad Momani, Mohd Alauddin Mohd Ali, Norbahiah Misran, Kazuo Shiokawa, Yuichi Otsuka, Kiyohumi Yumoto

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 71 ( 17-18 ) page： 1992 - 2005 2009.12

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

This paper investigates the ionospheric and geomagnetic responses during the 28 March 2005 and 14 May 2005 Sumatran earthquakes using GPS and magnetometer stations located in the near zone of the epicenters. These events occurred during low solar and geomagnetic activity. TEC oscillations with periods of 5-10 min were observed about 10-24 min after the earthquakes and have horizontal propagation velocities of 922-1259 m/s. Ionospheric disturbances were observed at GPS stations located to the northeast of the epicenters, while no significant disturbances were seen relatively east and south of the epicenters. The magnetic field measurements show rapid fluctuations of 4-5 s shortly after the earthquake, followed by a Pc5 pulsation of 4.8 min about 11 min after the event. The correlation between the ionospheric and geomagnetic responses shows a good agreement in the period and time lag of the peak disturbance arrival, i.e. about 11-13 min after the earthquake. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jastp.2009.09.004

Spatial relationship of F-region field-aligned irregularities and medium-scale traveling ionospheric disturbances observed with the MU radar and all-sky airglow imagers Reviewed

Otsuka Y., Shiokawa K., Ogawa T., Yokoyama T., Yamamoto M.

ICCAS-SICE 2009 - ICROS-SICE International Joint Conference 2009, Proceedings page： 1310 - 1311 2009.12

Language：English Publishing type：Research paper (scientific journal) Publisher：ICCAS-SICE 2009 - ICROS-SICE International Joint Conference 2009, Proceedings

We report simultaneous observations of medium-scale traveling ionospheric disturbances (MSTIDs) and field-aligned irregularities (FAIs) in the F region by using two all-sky airglow imagers and the MU radar in Japan. MSTIDs propagating southwestward were observed in 630-nm airglow images on the night of June 16, 2004. During this MSTID event, FAIs in the F region were observed by making multibeam measurements with the MU radar. We found that FAIs with intense (weak) signal-to-noise ratio (SNR) coincided with the airglow depletion (enhancement) caused by the MSTIDs. This result indicates that the FAIs could be generated by the gradient drift instability at the airglow depletion region. © 2009 SICE.

The optical mesosphere thermosphere imagers (OMTIs) for network measurements of aurora and airglow Reviewed

Shiokawa K., Hosokawa K., Sakaguchi K., Ieda A., Otsuka Y., Ogawa T., Connors M.

Aip Conference Proceedings Vol. 1144 page： 212 - 215 2009.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Aip Conference Proceedings

The Optical Mesosphere Thermosphere Imagers (OMTIs) currently consist of eight all-sky cooled-CCD imagers and several interferometers and spectrometers. They are making routine observations of aurora and airglow in Japan, Australia, Indonesia, and Canada. Here we show recent results of OMTIs particularly from the two Canadian stations at Resolute Bay (RSB) and Athabasca (ATH). At RSB, we observe polar-cap plasma patches almost always during southward IMF periods. From two-dimensional cross-correlation analyses, we determine velocity vectors of the patches, which indicates the ionospheric convection vector, showing high correlation with the IMF-By and -Bz variations. At ATH, we often observe isolated proton arcs and Stable Auroral Red (SAR) arcs, which are located equatorward of the auroral oval. The appearance of the isolated proton arcs is highly correlated with the Pc 1 geomagnetic pulsations measured simultaneously at ATH, suggesting interactions between the electromagnetic ion cyclotron (EMIC) waves and protons in the vicinity of the plasmapause and the ring current. Similar interactions without waves are also suggested for the SAR arcs, which appear after the substorm expansion phase even without geomagnetic storms. These observations show promising capability to monitor magnetospheric processes from the ground stations, which would contribute to the future satellite projects, such as THEMIS, ERG, and Scope/Xscale. © 2009 American Institute of Physics.

DOI： 10.1063/1.3169292

プラズマバブルに伴うGPSにおけるロック損失分布・全電子数変化率分布の時間変化 Reviewed

菊地隼人, 中田裕之, 津川卓也, 大塚雄一, 鷹野敏明, 島倉信, 塩川和夫, 小川忠彦

大気電気学会誌 = / Society of Atmospheric Electricity of Japan Vol. 3 ( 2 ) page： 68 - 69 2009.10

Coordinated observations of nighttime medium-scale traveling ionospheric disturbances in 630-nm airglow and HF radar echoes at midlatitudes Reviewed Open Access

S. Suzuki, K. Hosokawa, Y. Otsuka, K. Shiokawa, T. Ogawa, N. Nishitani, T. F. Shibata, A. V. Koustov, B. M. Shevtsov

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 114 ( 7 ) 2009.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We investigate nighttime medium-scale traveling ionospheric disturbances (MSTIDs) using the SuperDARN HF radar at Hokkaido, Japan (43.5 degrees N, 143.6 degrees E), and an OI 630-nm airglow imager located at Paratunka, Russia (53.0 degrees N, 158.2 degrees E), within the radar field of view. The imager identified southwestward propagating MSTIDs with a horizontal wavelength of similar to 300 km on 8 December 2007. Throughout this event, the radar continuously detected ionospheric echoes originating from decameter-scale field-aligned irregularities (FAIs) at the F region heights. The Doppler velocities of these echoes showed systematic polarity changes which were consistent with airglow intensity variations. These polarity changes would be attributed to E x B plasma drifts caused by the polarization electric field embedded in the MSTIDs. The FAI echo powers also varied in agreement with the airglow intensity variations: strong (weak) echoes coincided with the airglow depletion (enhancement) region. Considering the MSTID polarization electric field, it is suggested that the observed FAIs were generated by the gradient drift instability on the bottomside of the F region.

DOI： 10.1029/2008JA013963

Spatial relationship of nighttime medium-scale traveling ionospheric disturbances and F region field-aligned irregularities observed with two spaced all-sky airglow imagers and the middle and upper atmosphere radar Reviewed Open Access

Otsuka Y, Shiokawa K, Ogawa T, Yokoyama T, Yamamoto M

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 114 ( 5 ) 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

We report simultaneous observations of medium-scale traveling ionospheric disturbances (MSTIDs) and field-aligned irregularities (FAls) in the F region using two all-sky airglow imagers and the middle and upper atmosphere (MU) radar. MSTIDs propagating southwestward were observed simultaneously in 630-nm airglow images over Sakata (39.0°N, 139.9°E) and Shigaraki (34.90N, 136.1°E), Japan, on the night of 16 June 2004. By using all-sky images over both sites, we estimated the altitude of the airglow layer to be 260 km by the triangulation method. During the MSTID event, FAIs in the F region were observed by making multibeam measurements with the MU radar at Shigaraki. In order to investigate the spatial relationship between the MSTIDs and FAIs, the FAIs were mapped onto the 630-nm airglow layer (altitude, 260 km) along the geomagnetic field lines. We found that FAIs with an intense (weak) signal-to-noise ratio coincided with the airglow depletion (enhancement) caused by the MSTIDs. FAI velocity obtained from a combination of the Doppler velocities on the three radar beams oscillated in the northwest-southeast direction, with an amplitude of approximately 82 m/s. The FAI velocity was northwestward (southeastward) at the airglow depletion (enhancement). The directions of the FAI velocity were consistent with those of the ExB drifts caused by the polarized electric fields associated with the MSTIDs. The northeastward polarized electric field at the airglow depletion region strengthened the background eastward effective electric field and drove the gradient drift instability generating FAIs. This might be the reason why the FAIs preferred to occur at the airglow depletion region. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2008JA013902

Other Link： http://orcid.org/0000-0001-8392-6455

Motion of polar cap patches: A statistical study with all-sky airglow imager at Resolute Bay, Canada Reviewed Open Access

Hosokawa, K, Kashimoto, T, Suzuki, S, Shiokawa, K, Otsuka, Y, Ogawa, T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 114 ( 4 ) 2009.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

A highly sensitive all-sky airglow imager (part of the Optical Mesosphere Thermosphere Imagers [OMTIs]) has been operating for 3 years at Resolute Bay, Canada (geographic latitude 74.7 degrees N; geomagnetic latitude 82.9 degrees N) since January 2005. One of its major applications is the observation of polar cap patches. Polar cap patches are generated in the vicinity of the cusp during southward interplanetary magnetic field (IMF) conditions, and they exhibit dynamic movement, possibly in association with the changes in the IMF orientation. In order to determine how their motions are controlled by the upstream IMF conditions, we applied a motion-tracking algorithm that was based on two-dimensional cross-correlation analysis to consecutive images obtained from January 2005 to December 2007 by the all-sky airglow imager at Resolute Bay. We identified and extracted 561 individual patches and then carried out a statistical study of their motion. It is demonstrated that the speed of patches is primarily controlled by the IMF B(z). Furthermore, the dawn-dusk component of the patch drift velocities is well correlated with the IMF B(y), which is in good agreement with the published By dependence of the nightside polar cap convection. This enables us to monitor the plasma convection within the polar cap by using polar cap patches as tracers.

DOI： 10.1029/2008JA014020

Unusually elongated, bright airglow plume in the polar cap F region: Is it a tongue of ionization? Reviewed

K. Hosokawa, T. Tsugawa, K. Shiokawa, Y. Otsuka, T. Ogawa, M. R. Hairston

GEOPHYSICAL RESEARCH LETTERS Vol. 36 ( 7 ) 2009.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report an event of unusually elongated, bright airglow plume, which is considered as an optical manifestation of tongue of ionization (TOI) in the central polar cap. This optical structure was detected with an all-sky airglow imager at Resolute Bay (74.73 degrees N, 265.07 degrees E) during a large magnetic storm on December 15, 2006. The absolute optical intensity of the plume was approximate to 1 kR, which is much brighter than that of non-stormtime polar cap patches. Two-dimensional imaging capability of the all-sky imager demonstrates that some meso-scale structures (approximate to 250-600 km) were embedded within the plume. Simultaneous ion density and drift measurements with the DMSP spacecraft strongly suggest that the plume was extending from the dayside as a narrow stream of dense plasma and thus is an optical manifestation of polar cap TOI. The DMSP data also implies that the possible source of the plume is a narrow stream of storm enhanced density (SED) transported from lower latitudes. The DMSP auroral particle observation demonstrates that the polar cap extremely expanded equatorward during this interval. This extreme expansion allowed the anti-sunward convection to capture plasmas within the SED and deliver them deep into the polar cap as a luminous airglow plume. This observation claims that the plasma transport from the dayside lower latitudes plays an important role in controlling the plasma environment in the polar cap ionosphere during magnetic storms. Citation: Hosokawa, K., T. Tsugawa, K. Shiokawa, Y. Otsuka, T. Ogawa, and M. R. Hairston (2009), Unusually elongated, bright airglow plume in the polar cap F region: Is it a tongue of ionization?, Geophys. Res. Lett., 36, L07103, doi:10.1029/2009GL037512.

DOI： 10.1029/2009GL037512

Super plasma fountain and equatorial ionization anomaly during penetration electric field Reviewed Open Access

Balan, N, Shiokawa, K, Otsuka, Y, Watanabe, S, Bailey, GJ

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 114 ( 3 ) 2009.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

Relative importance of diffusion, electric field, and neutral wind on equatorial plasma fountain and equatorial ionization anomaly (EIA) during a strong daytime eastward prompt penetration electric field (PPEF) event are evaluated using the Sheffield University Plasmasphere Ionosphere Model and the recorded PPEF during the super geomagnetic storm of 9 November 2004. The fountain rapidly develops into a super fountain during the PPEF event. The super fountain becomes strong with less poleward turning of the velocity vectors in the presence of an equatorward wind that reduces (or stops) the downward velocity component due to diffusion and raises the ionosphere to high altitudes of reduced chemical loss. The EIA crests in peak electron density and total electron content shift rapidly to higher than normal latitudes during the PPEF event. However, the crests become stronger than normal only in the presence of an equatorward wind. The results suggest that the presence of an equatorward neutral wind is required to produce a strong positive ionospheric storm during, a daytime eastward PPEF event. The equatorward neutral wind need not be a storm time wind though stronger wind can lead to stronger ionospheric storms. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2008JA013768

Relationship between polar cap patches and field-aligned irregularities as observed with an all-sky airglow imager at Resolute Bay and the PolarDARN radar at Rankin Inlet Reviewed Open Access

K. Hosokawa, K. Shiokawa, Y. Otsuka, T. Ogawa, J. P. St-Maurice, G. J. Sofko, D. A. Andre

Journal of Geophysical Research: Space Physics Vol. 114 ( 3 ) 2009.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

Simultaneous two-dimensional observations of airglow enhancement and radar backscatter from field-aligned irregularities (FAIs) associated with polar cap patches were conducted. The spatial structure of 630 nm airglow from polar cap patches was imaged using an all-sky airglow imager at Resolute Bay, Canada, while backscatter echoes from decameter-scale FAIs were observed using the newly constructed HF Polar Dual Auroral Radar Network (PolarDARN) radar at Rankin Inlet, Canada. Both the airglow enhancement and the radar backscatter appeared within a structured region with the spatial extent of about 500-1000 km. The decameter-scale FAIs were found to extend over the entire region of airglow enhancement associated with polar cap patches, indicating that the polar patch plasma became almost fully structured soon after initiation (within approximately 2025 min). These findings imply that some rapid structuring process of the entire patch area is involved in addition to the primary gradient-drift instabilities. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2008JA013707

赤道プラズマバブルに伴うGPSでのロック損失と全電子数変化率分布 Reviewed

Measurements of geomagnetically induced current in a power grid in Hokkaido, Japan Reviewed Open Access

Watari S, Kunitake M, Kitamura K, Hori T, Kikuchi T, Shiokawa K, Nishitani N, Kataoka R, Kamide Y, Aso T, Watanabe Y, Tsuneta Y

Space Weather Vol. 7 ( 3 ) page： S03002 2009.3

菊地隼人, 中田裕之, 津川卓也, 大塚雄一, 鷹野敏明, 島倉信, 塩川和夫, 小川忠彦

大気電気学会誌 = / Society of Atmospheric Electricity of Japan Vol. 3 ( 1 ) page： 126 - 127 2009.3

Medium-scale traveling ionospheric disturbances observed with the SuperDARN Hokkaido radar, all-sky imager, and GPS network and their relation to concurrent sporadic E irregularities Reviewed Open Access

T. Ogawa, N. Nishitani, Y. Otsuka, K. Shiokawa, T. Tsugawa, K. Hosokawa

Journal of Geophysical Research: Space Physics Vol. 114 ( 3 ) 2009.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

We present midlatitude medium-scale traveling ionospheric disturbances (MSTIDs) observed with a Super Dual Auroral Radar Network (SuperDARN) HF radar at around 10 MHz in Hokkaido, Japan, in combination with a 630-nm all-sky imager and a GPS network (GEONET) that provides total electron content (TEC) data. MSTIDs propagating southward from high latitudes are detected at first with the HF radar and then with the imager and GEONET. We analyze two MSTID events, one in winter (event 1) and the other in summer (event 2), to find that MSTIDs appear simultaneously, at least, at 55°-25°N. It is shown that nighttime MSTIDs propagate toward the southwest over a horizontal distance of about 4000 km, and daytime MSTIDs do so toward the southeast. Daytime radar echoes are due to ground/sea surface (GS) scatter, while nighttime echoes in event 1 return from 15-m-scale F region field-aligned irregularities (FAIs) and those in event 2 are due to GS scatter. Doppler velocities of the nighttime F region FAI echoes in event 1 are negative (motion away from the radar) within strong echo regions and are positive (motion toward the radar) within weak echo regions. This fact suggests that the strong (weak) echoes return from suppressed (enhanced) airglow/TEC areas, in line with previous observations over central Japan. The nighttime MSTIDs in events 1 and 2 are often accompanied by concurrent coherent echoes from FAIs in sporadic E (Es) layers. The Es echo areas in event 2 rather coincide with suppressed airglow/TEC areas in the F region that are connected with the echo areas along the geomagnetic field, indicating the existence of E and F region coupling at night. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2008JA013893

Medium-Scale Traveling Ionospheric Disturbances and Plasma Bubbles Observed by an All-Sky Airglow Imager at Yonaguni, Japan Reviewed

Tadahiko Ogawa, Yuichi Otsuka, Kazuo Shiokawa, Takuya Tsugawa, Akinori Saito, Kazuaki Hoshinoo, Keisuke Matunaga, Minoru Kubota, Mamoru Ishii

TERRESTRIAL ATMOSPHERIC AND OCEANIC SCIENCES Vol. 20 ( 1 ) page： 287 - 295 2009.2

Language：English Publishing type：Research paper (scientific journal) Publisher：CHINESE GEOSCIENCE UNION

We report on nighttime airglow imaging observations of the low latitude ionosphere by means of a 630-m all-sky imager installed in March 2006 at Yonaguni, Japan (24.5 degrees N, 123.0 degrees E; 14.6 degrees N geomagnetic), about 100 kin east of Taiwan. The imager detected medium-scale traveling ionospheric disturbances (MSTIDs) for about 7 hours on the night of 26 May 2006. A dense GPS network in Japan also observed the same MSTID event on this night. The imager and GEONET data indicate that most of the MSTIDs propagated southwestward from the north of Japan to the south of Yonaguni and Taiwan over 4000 kin, with a southern limit of 19 degrees N (geomagnetic latitude 9 degrees N) or lower. On the night of 10 November 2006, the imager observed two weak emission bands that were embedded on the F-region anomaly crest to the south of Yonaguni. The simultaneous electron density profiles from the FORMOSAT-3/COSMIC mission demonstrate that the weak emission bands are due to density depletions in equatorial plasma bubbles. These case studies suggest that the Yonaguni imager in collaboration with other instruments is very suitable for the study of ionospheric disturbances in and around the northern F-region anomaly crest.

DOI： 10.3319/TAO.2007.12.06.02(F3C)

Statistical characteristics of polar cap mesospheric gravity waves observed by an all-sky airglow imager at Resolute Bay, Canada Reviewed Open Access

S. Suzuki, K. Shiokawa, K. Hosokawa, K. Nakamura, W. K. Hocking

Journal of Geophysical Research: Space Physics Vol. 114 ( 1 ) 2009.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

An airglow imager at Resolute Bay, Canada (74.7°N, 265.1°E) has been used for the observation of gravity waves in the polar cap mesosphere since January 2005. On the basis of the long-term imaging observations obtained over 137 nights during the winter seasons of 2005 and 2006, we extracted 143 events of small-scale (&lt
100 km) gravity waves from sequential sodium airglow (589.3 nm) images. The observed waves typically had horizontal wavelengths of 20-50 km and phase speeds of 30-60 ms-1. The propagation directions were predominantly westward. We also identified larger-scale (&gt
100 km) gravity waves using airglow keograms, which represent a time series of the horizontal cross sections of the airglow images. The horizontal wavelengths and phase speeds of the large-scale waves were typically 100-400 km and 60-100 ms -1, respectively. The propagation directions of these large-scale waves also showed a westward preference. The wave parameters appeared to have no relation with the geomagnetic activities represented by the Kp index. On the other hand, the propagation directions of the observed waves were consistent with the prevailing eastward winds in the mesosphere and the updraft associated with a low-pressure area that generally appears to the east of Resolute Bay at tropospheric altitudes. These results suggest that the main source of the gravity waves in the polar cap mesosphere is tropospheric dynamics rather than auroral activities. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2008JA013652

Effects observed in the ionospheric F region in the east Asian sector during the intense geomagnetic disturbances in the early part of November 2004 Reviewed Open Access

Y. Sahai, F. Becker-Guedes, P. R. Fagundes, R. De Jesus, A. J. De Abreu, Y. Otsuka, K. Shiokawa, K. Igarashi, K. Yumoto, C. S. Huang, H. T. Lan, A. Saito, F. L. Guarnieri, V. G. Pillat, J. A. Bittencourt

Journal of Geophysical Research: Space Physics Vol. 114 ( 3 ) 2009.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

The Sun was very active in the early part of November 2004. During the period of 8-10 November 2004, intense geomagnetic disturbances with two superstorms were observed. In a companion paper (hereinafter referred to as paper 1), the effects observed in the F region during the intense geomagnetic disturbances in the early part of November 2004 in the Latin American sector were presented. In the present paper, we investigate the effects observed in the F region during the intense geomagnetic disturbances in the early part of November 2004 in the east Asian sector. We have used the ionospheric sounding observations at Ho Chi Minh City (Vietnam) and Okinawa, Yamagawa, Kokubunji, and Wakkanai (Japan) in the present investigations. Also, GPS observations in the east Asian sector (several longitude zones) have been used to study the effect in the F region during the intense geomagnetic disturbances. The ion density versus latitudinal variations obtained by the DMSP F15 satellite orbiting at about 800 km altitude in the east Asian sector and the magnetic field data obtained at several stations in the Japanese meridian are also presented. Several important features from these observations in both the sectors during this extended period of intense geomagnetic disturbances are presented. The east Asian sector showed very pronounced effects during the second superstorm, which was preceded by two storm enhancements. It should be mentioned that around the beginning of the night on 10 November, ionospheric irregularities propagating from higher midlatitude region to low-latitude region were observed in the Japanese sector. The most intense geomagnetic field H component in that sector was observed on 10 November at L = 2.8, indicating that the auroral oval and the heating got further to low latitudes and the ionospheric irregularities observed in the Japanese sector on this night are midlatitude ionospheric disturbances associated with the second superstorm. The absence of ionospheric irregularities in the Japanese sector during the 8 November superstorm suggests that the magnetosphere-ionosphere system was possibly preconditioned (primed) when the second interplanetary structure impacted the magnetosphere. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2008JA013053

Equatorial GPS ionospheric scintillations over Kototabang, Indonesia and their relation to atmospheric waves from below Reviewed Open Access

Ogawa Tadahiko, Miyoshi Yasunobu, Otsuka Yuichi, Nakamura Takuji, Shiokawa Kazuo

EARTH PLANETS AND SPACE Vol. 61 ( 4 ) page： 397 - 410 2009

Fine structures and dynamics in auroral initial brightening at substorm onsets Reviewed Open Access

Sakaguchi K., Shiokawa K., Ieda A., Nomura R., Nakajima A., Greffen M., Donovan E., Mann I. R., Kim H., Lessard M.

ANNALES GEOPHYSICAE Vol. 27 ( 2 ) page： 623-630 2009

Propagation characteristics of nighttime mesospheric and thermospheric waves observed by optical mesosphere thermosphere imagers at middle and low latitudes Reviewed Open Access

Shiokawa K., Otsuka Y., Ogawa T.

EARTH PLANETS AND SPACE Vol. 61 ( 4 ) page： 479-491 2009

28pSP-16 Precipitation of radiation belt relativistic electrons by electromagnetic ion cyclotron waves Reviewed Open Access

Miyoshi Y., Sakaguchi K., Shiokawa K., Evans D., Albert J., Connors M., Jordanova V.

Meeting Abstracts of the Physical Society of Japan Vol. 64.1.2 ( 0 ) page： 228 2009

Characteristics of equatorial gravity waves derived from mesospheric airglow imaging observations Reviewed Open Access

Suzuki S., Shiokawa K., Liu A. Z., Otsuka Y., Ogawa T., Nakamura T.

ANNALES GEOPHYSICAE Vol. 27 ( 4 ) page： 1625 - 1629 2009

New observational deployments for SEALION-Airglow measurements using all-sky imagers Reviewed Open Access

Minoru Kubota, Mamoru Ishii, Takuya Tsugawa, Jyunpei Uemoto, Hidekatsu Jin, Yuichi Otsuka, Kazuo Shiokawa

Journal of the National Institute of Information and Communications Technology Vol. 56 ( 1-4 ) page： 299 - 307 2009

Language：English Publishing type：Research paper (scientific journal)

An airglow all-sky imager (ASI)-a new monitoring instrument-is scheduled to be set up in February 2010 at Chiang Mai, Thailand, as part of the framework of the Southeast Asia Low-latitude Ionospheric Network (SEALION) being developed in the Southeast Asian region by the National Institute of Information and Communications Technology (NICT). The ASI images airglow having an emission layer near the ionospheric F-layer in order to observe the two-dimensional structure and time evolution of such ionospheric disturbances as plasma bubbles. In Southeast Asia, the Solar-Terrestrial Environment Laboratory (STE) of Nagoya University has been conducting ASI-based observations at Kototabang, Indonesia, ever since 2002. This paper provides detailed insight into the formation, growth and propagation of plasma bubbles as derived from observational data recorded using ASI at Kototabang and using SEALION ionoson-des and GPS receivers. The functional requirements for another ASI to be installed and ASI-based observation schemes are then discussed based on that insight.

Joint observations of a traveling ionospheric disturbance with the Paratunka OMTI camera and the Hokkaido HF radar Reviewed Open Access

Koustov A., Nishitani N., Ponomarenko P. V., Shiokawa K., Suzuki S., Shevtsov B. M., MacDougall J. W.

ANNALES GEOPHYSICAE Vol. 27 ( 6 ) page： 2399 - 2406 2009

Effects of geomagnetically induced current on power grids Reviewed

Watari S, Kunitake M, Kitamura K, Hori T, Kikuchi T, Shiokawa K, Nishitani N, Kataoka R, Kamide Y, Watanabe Y

Journal of the National Institute of Information and Communications Technology Vol. 56 ( 1-4 ) page： 125 - 133 2009

Language：English Publishing type：Research paper (scientific journal)

There have been many reports that geomagnetically induced current (GIC) has affected the operation of electric power grids. Given Japan's location at lower geomagnetic latitude than its geographic latitude, the effects of GIC on electric power grids there are believed to be small, but have yet to be subjected to elaborate analysis. This paper describes the results of GIC measured in Hokkaido over a two-year period in collaboration with the National Institute of Information and Communications Technology (NICT), Hokkaido Electric Power Co., Inc., and the Solar- Terrestrial Environment Laboratory (STEL) of Nagoya University.

ULF geomagnetic anomalous changes possibly associated with 2004-2005 Sumatra earthquakes Reviewed

Other Link： http://orcid.org/0000-0001-8451-6941

S. Saroso, K. Hattori, H. Ishikawa, Y. Ida, R. Shirogane, M. Hayakawa, K. Yumoto, K. Shiokawa, M. Nishihashi

PHYSICS AND CHEMISTRY OF THE EARTH Vol. 34 ( 6-7 ) page： 343 - 349 2009

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Anomalous ULF geomagnetic field change is considered to be one of the most convincing and promising phenomena among earthquake-related electromagnetic effects, because we expect emissions from the crust of the source region. There has been a great deal of accumulated and convincing evidence of ULF magnetic signatures before large earthquakes as reported in the previous studies. In order to verify these phenomena preceding large earthquakes and to clarify the relationship between electromagnetic phenomena and possible physical mechanism, we have investigated the data of ULF geomagnetic observations at Kototabang and Biak stations associated with the 2004/2005 Sumatra earthquakes. A case study is carried out in this work to investigate the pre-earthquake ULF geomagnetic anomalies during the Sumatra-Andaman earthquake on December 26, 2004 (magnitude Mw = 9.0 and depth = 30 km from USGS catalog), and Sumatra-Nias earthquake on March 28, 2005 (Mw = 8.7 and depth = 30 km). For the aim of finding any precursors, we have adopted the spectral density ratio analysis and transfer functions analysis based on wavelet transform method. Results of the spectral density analysis indicate similar variations to those of amplitude for the induction arrow in transfer function analysis. Both of these variations at Kototabang exhibit strange or anomalous changes from a few weeks before the Sumatra-Andaman earthquake to July 2005, while there are no apparent changes at remote station of Biak. To make these results more convincing, the fractal analysis based on a Higuchi method has been applied to the same observed data, which also show a significant change (or decrease) in mono-fractal dimension a few weeks before the earthquakes. This result would lend a further support to those by the spectral density ratio and transfer function analyses. So, we can conclude that the anomalous change as observed simultaneously by the three methods, might be a possible signature related with the earthquake preparation phase of Sumatra earthquakes. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.pce.2008.10.065

Northeastward motion of nighttime medium-scale traveling ionospheric disturbances at middle latitudes observed by an airglow imager Open Access

Longitudinal development of a substorm brightening arc Reviewed Open Access

Shiokawa K., Ieda A., Nakajima A., Sakaguchi K., Nomura R., Aslaksen T., Greffen M., Spanswick E., Donovan E., Mende S. B., McFadden J., Glassmeier K. -H., Angelopoulos V., Miyashita Y.

ANNALES GEOPHYSICAE Vol. 27 ( 5 ) page： 1935 - 1940 2009

The Upper Atmosphere and Plasma Imager/the Telescope of Visible Light (UPI/TVIS) onboard the Kaguya spacecraft Reviewed Open Access

Taguchi M., Sakanoi T., Okano S., Kagitani M., Kikuchi M., Ejiri M., Yoshikawa I., Yamazaki A., Murakami G., Yoshioka K., Kameda S., Miyake W., Nakamura M., Shiokawa K.

EARTH PLANETS AND SPACE Vol. 61 ( 12 ) page： XVII - XXIII 2009

Possible influence of ultra-fast Kelvin wave on the equatorial ionosphere evening uplifting Reviewed Open Access

Takahashi H., Abdu M. A., Wrasse C. M., Fechine J., Batista I. S., Pancheva D., Lima L. M., Batista P. P., Clemesha B. R., Shiokawa K., Gobbi D., Mlynczak M. G., Russell J. M.

EARTH PLANETS AND SPACE Vol. 61 ( 4 ) page： 455 - 462 2009

K. Shiokawa, Y. Otsuka, N. Nishitani, T. Ogawa, T. Tsugawa, T. Maruyama, S. E. Smirnov, V. V. Bychkov, B. M. Shevtso

Journal of Geophysical Research: Space Physics Vol. 113 ( A12 ) 2008.12

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed in 630-nm airglow images at middle latitudes are known to have a predominantly northwest-southeast phase surface and to move southwestward in the Northern Hemisphere of Earth. However, the mechanisms of MSTID generation and their systematic southwestward motion have not been clarified. In this paper, we report the "northeastward" motion of the MSTIDs observed at Paratunka, Far East Russia (52.97°N, 158.25°E), using an all-sky 630-nm airglow imager at 2000-2300 LT on 19 August 2007. The MSTIDs moved first southwestward but then back northeastward in the northern part of the images. The northeastward motion of the MSTIDs took place coincident with a F layer height decrease observed by an ionosonde at Paratunka. The F layer height decrease was also confirmed by an enhancement of the 630-nm airglow intensity, which seemed to propagate from northeast to southwest. This fact suggests that the F layer height decrease was caused by poleward wind enhancement rather than westward electric field. These observations imply that the F layer height decrease or the poleward thermospheric wind has some role in the northeastward turning of the MSTID propagation direction. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2008JA013417

Precipitation of radiation belt electrons by EMIC waves, observed from ground and space Reviewed Open Access

Y. Miyoshi, K. Sakaguchi, K. Shiokawa, D. Evans, J. Albert, M. Connors, V. Jordanova

GEOPHYSICAL RESEARCH LETTERS Vol. 35 ( 23 ) 2008.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We show evidence that left-hand polarised electromagnetic ion cyclotron (EMIC) plasma waves can cause the loss of relativistic electrons into the atmosphere. Our unique set of ground and satellite observations shows coincident precipitation of ions with energies of tens of keV and of relativistic electrons into an isolated proton aurora. The coincident precipitation was produced by wave-particle interactions with EMIC waves near the plasmapause. The estimation of pitch angle diffusion coefficients supports that the observed EMIC waves caused coincident precipitation of both ions and relativistic electrons. This study clarifies that ions with energies of tens of keV affect the evolution of relativistic electrons in the radiation belts via cyclotron resonance with EMIC waves, an effect that was first theoretically predicted in the early 1970's.

DOI： 10.1029/2008GL035727

Simultaneous THEMIS in situ and auroral observations of a small substorm Reviewed

E. Donovan, W. Liu, J. Liang, E. Spanswick, I. Voronkov, M. Connors, M. Syrjasuo, G. Baker, B. Jackel, T. Trondsen, M. Greffen, V. Angelopoulos, C. T. Russell, S. B. Mende, H. U. Frey, A. Keiling, C. W. Carlson, J. P. McFadden, K. -H. Glassmeier, U. Auster, K. Hayashi, K. Sakaguchi, K. Shiokawa, J. A. Wild, I. J. Rae

GEOPHYSICAL RESEARCH LETTERS Vol. 35 ( 17 ) 2008.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We present ground-based and in situ observations from March 13, 2007. The THEMIS satellites were in the evening sector conjugate to THEMIS ground-based imagers. At similar to 0507 UT there was an optical onset on inner CPS field lines. This involved near-simultaneous brightening of 1 MLT hour longitudinal segment of the onset arc. The part of the arc that brightened was that closest to the equatorward boundary of the diffuse ( proton) aurora. Within one minute, a dipolarization front moved across four THEMIS satellites. Based on their locations, the order in which they detected the dipolarization front, and the auroral evolution, we assert that the expansion phase began earthward of the four satellites and evolved radially outwards. We conclude that this onset occurred in an azimuthally localized region of highly stretched field lines.

DOI： 10.1029/2008GL033794

Particle and field characteristics of broadband electrons observed by the FAST satellite during geomagnetic storms: A multievent study Reviewed Open Access

A. Nakajima, K. Shiokawa, K. Seki, J. P. McFadden, C. W. Carlson, R. J. Strangeway, K. Yumoto

Journal of Geophysical Research: Space Physics Vol. 113 ( A6 ) 2008.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

During geomagnetic storms, remarkable electron-flux enhancements (&gt
1012 eV cm-2 s-1) over a broadband energy range (∼0.05-10 keV) are sometimes observed near the equatorward edge of the auroral oval. We call such electron flux enhancements broadband electrons (BBEs). In this paper, we identified 12 BBE events from the electron-energy spectra obtained by the Fast Auroral Snapshot (FAST) satellite during 81 large geomagnetic storms (minimum Dst index &lt
-90 nT) between September 1996 and March 2004. Ground-based magnetic field data show that the BBEs are observed ∼6-28 min after the onset of substorms during the main phase of large storms. During these events, the pitch angle distributions of electrons show isotropic features at a higher energy range above ∼1 keV, except for an upward loss cone. At a lower energy range below ∼1 keV, field-aligned downward electron fluxes are most intense, and perpendicular fluxes are weakest. These results imply that a higher-energy part of BBEs originates from higher altitudes in the inner magnetosphere and that a lower-energy part is accelerated parallel to the local magnetic field at lower altitudes near the satellite. Intense fluctuations of electric and magnetic fields and enhanced lower-frequency (0.1 Hz to 16 kHz) waves are observed during the BBEs. These characteristics are common for all BBE events. We compared lower-energy (&lt
1 keV) electron fluxes with field-aligned Poynting fluxes of the waves at 0.06-4 Hz during the BBEs. The Poynting fluxes are systematically downward with intensity comparable to that of the lower-energy electron fluxes, suggesting downward acceleration of lower-energy electrons by the observed low-frequency waves. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JA013001

Correlation of substorm injections, auroral modulations, and ground Pi2 Reviewed Open Access

A. Keiling, V. Angelopoulos, D. Larson, R. Lin, J. McFadden, C. Carlson, J. W. Bonnell, F. S. Mozer, K. -H. Glassmeier, H. U. Auster, W. Magnes, S. Mende, H. Frey, A. Roux, O. LeContel, S. Frey, T. Phan, E. Donovan, C. T. Russell, I. Mann, W. Liu, X. Li, M. Fillingim, G. Parks, K. Shiokawa, J. Raeder

GEOPHYSICAL RESEARCH LETTERS Vol. 35 ( 17 ) 2008.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

In this case study we report a substorm, 23 March 2007, which exhibited oscillations with a period of similar to 135 s in three substorm phenomena all of which were one-to-one correlated. The in-situ observations are from one THEMIS spacecraft (8.3 R(E) geocentric distance) and the geosynchronous LANL-97A spacecraft. The focus here is on the intensification phase during which THEMIS was conjugate to the region of auroral brightening and its foot point was near the high-latitude ground station Kiana. The following results will be demonstrated: (1) THEMIS and LANL-97A (time-delayed) recorded periodic ion injections (> 100 keV). (2) Near-conjugate high-latitude ground magnetometer data show very large Pi2 (delta H similar to 150\ nT) with a 6-s time delay compared to the THEMIS ion injections. (3) Low-latitude ground magnetometer data also show Pi2 with the same waveform as the high-latitude Pi2 but with longer time delays (20-31 s). (4) Auroral luminosity was periodically modulated during the intensification phase. (5) All three signatures (ion injections, ground Pi2, optical modulation) had the same periodicity of similar to 135 s but with various time delays with respect to the THEMIS ion injections. These observations demonstrate that the three substorm phenomena had a common source which controlled the periodicity.

DOI： 10.1029/2008GL033969

プラズマバブルの発生位置の同定 Reviewed

木下佳紀, 中田裕之, 大塚雄一, 鷹野敏明, 島倉信, 塩川和夫, 小川忠彦

大気電気学会誌 Vol. 2 ( 1 ) page： 147 - 148 2008.5

Simultaneous appearance of isolated auroral arcs and Pc 1 geomagnetic pulsations at subauroral latitudes Reviewed Open Access

K. Sakaguchi, K. Shiokawa, Y. Miyoshi, Y. Otsuka, T. Ogawa, K. Asamura, M. Connors

Journal of Geophysical Research: Space Physics Vol. 113 ( A5 ) 2008.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

We have been conducting observations of aurora and geomagnetic pulsations at Athabasca, Canada, located at a subauroral latitude (magnetic latitude: 62°, L ∼ 4.6), using an all-sky imager and an induction magnetometer. Isolated auroral arcs at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm (H β) were often observed at latitudes separated equatorward from the main auroral oval. From a 1-year observation (4 September 2005 to 3 September 2006), we found 13 isolated arc events. All these isolated arcs occurred coincidentally with Pc 1 geomagnetic pulsations, although there were nine other Pc 1 events without isolated arcs in the field of view of the imager. The arcs were observed in both pre- and post-midnight sectors and tended to appear during the late recovery phase of geomagnetic storms. The isolated arcs had limited latitudinal and longitudinal widths of less than 230 km and 250-800 km, respectively. We found that as isolated arcs moved equatorward (poleward), the frequencies of the simultaneous Pc 1 pulsations increased (decreased). Using the Tsyganenko-02 magnetic field model, the observed Pc 1 frequencies were almost the same as the frequencies of He+ electromagnetic ion cyclotron (EMIC) waves at the equatorial plane connected to observed isolated arcs. These results indicate that interactions of spatially localized EMIC waves with ring current ions cause high-energy ion precipitation and associated isolated auroras at subauroral latitudes. These results also imply that the dynamics and instabilities in the inner magnetosphere can be monitored as low-latitude auroral emissions away from the ordinary auroral oval. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JA012888

Atmospheric gravity waves identified by ground-based observations of the intensity and rotational temperature of OH airglow Reviewed

Suzuki H., Shiokawa K., Tsutsumi M., Nakamura T., Taguchi M.

Polar Science Vol. 2 ( 1 ) page： 1 - 8 2008.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Polar Science

Spectroscopic observations of OH airglow undertaken on May 2, 2006 at Uji, Japan reveal variations in intensity and rotational temperature related to the passage of an atmospheric gravity wave. The variations exhibit a period of approximately 1 h and magnitudes of 2-6% in intensity and 0.5-2% in rotational temperature. The vertical wavelength and intrinsic frequency of the atmospheric gravity wave were determined from the horizontal wavelength derived by an OH airglow imager, the background horizontal wind velocity obtained by the middle and upper atmosphere (MU) radar, and the dispersion relationship. The observed variations are consistent with the values calculated using the model of Liu, A.Z., Swenson, G.R. [2003. A modeling study of O2 and OH airglow perturbations induced by atmospheric gravity waves. J. Geophys. Res. 108 (No. D4), 4151. doi:10.1029/2002JD002474]. © 2008 Elsevier B.V. and NIPR.

DOI： 10.1016/j.polar.2007.12.002

Optical and radio observations and AMIE/TIEGCM modeling of nighttime traveling ionospheric disturbances at midlatitudes during geomagnetic storms

Fluctuation of intensity and rotational temperature of OH airglow caused by acoustic gravity waves Reviewed

Suzuki, H, K. Shiokawa, M. Tsutsumi, T. Nakamura, M. Taguchi

Polar Sci. Vol. 2 page： 1 - 8 2008.1

Development of an automatic procedure to estimate the reflection height of tweek atmospherics Reviewed Open Access

Ohya Hiroyo, Shiokawa Kazuo, Miyoshi Yoshizumi

EARTH PLANETS AND SPACE Vol. 60 ( 8 ) page： 837 - 843 2008

Rankin Inlet PolarDARN radar observations of duskward moving Sun-aligned optical forms Reviewed Open Access

Koustov A., Hosokawa K., Nishitani N., Ogawa T., Shiokawa K.

ANNALES GEOPHYSICAE Vol. 26 ( 9 ) page： 2711-2723 2008

K. Shiokawa, T. Tsugawa, T. Tsugawa, Y. Otsuka, T. Ogawa, G. Lu, A. Saito, M. Yamamoto

Geophysical Monograph Series Vol. 181 page： 271 - 281 2008

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

© 2008 by the American Geophysical Union. This paper summarizes our recent observations of storm-time traveling ionospheric disturbances (TIDs) over Japan. The storm-time TIDs, which are often referred as large-scale TIDs or traveling atmospheric disturbances, are generated at high-latitude auroral zone and propagate predominantly equatorward at midlatitudes as atmospheric waves in the thermosphere. The imaging measurements by airglow imagers and GPS networks give reliable wave parameters (wavelength, phase velocity, and amplitude) of TIDs. Comparison of imaging observations of TIDs between the northern and southern hemispheres revealed their nonconjugacy. Combinations of these imaging observations with vertical sounding measurements by ionosondes and radars provide a comprehensive description of TID structures at midlatitudes. Comparison between these observations and the assimilative mapping of the ionospheric electrodynamics technique with the thermosphere-ionosphere electrodynamics general circulation model results in several insights into the generation and propagation of TIDs at the high-latitude source region as well as limitations of the current global model.

DOI： 10.1029/181GM24

Simultaneous observations of nighttime medium-scale traveling ionospheric disturbances and E region field-aligned irregularities at midlatitude Reviewed Open Access

Otsuka, Y, Onoma, F, Shiokawa, K, Ogawa, T, Yamamoto, M, Fukao, S

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 112 ( A6 ) 2007.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

We report on simultaneous observations of very high frequency (VHF) radar backscatter from field-aligned irregularities (FAI) in the E region and medium-scale traveling ionospheric disturbances (MSTID) in 630-nm airglow images. On the night of 6 August 2002, the powerful 46.5-MHz middle and upper atmosphere (MU) radar with five beam directions at Shigaraki, Japan, observed typical quasiperiodic (QP) echoes from FAI in the E region. During this QP echo event, an all-sky charge-coupled device imager at the MU radar site detected MSTID in 630-nm airglow images. The MSTID also propagated southwestward at 80 m/s with fluctuation amplitudes of 50% from the background intensity and a wavelength of 380 km. Period of the MSTID was almost same as that of the Doppler velocity in the QP echoes. The airglow enhancement (depletion) caused by the MSTID coincided with southeastward (northwestward) velocity in the QP echo. These results indicate that the electric fields associated with the F region MSTID could be closely coupled to those associated with QP echoes in the E region. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2005JA011548

Particle and field characteristics of broadband electrons observed by the FAST satellite during a geomagnetic storm Reviewed Open Access

A. Nakajima, K. Shiokawa, K. Seki, R. J. Strangeway, J. P. McFadden, C. W. Carlson

Journal of Geophysical Research: Space Physics Vol. 112 ( A6 ) 2007.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

Broadband electrons (BBEs) are remarkable flux enhancements (&gt
10 13 eV cm-2 s-1) of precipitating electrons over a broad energy range (0.03-30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. We show characteristics of particles (energy spectra and pitch angle distribution) and fields (electric field, magnetic field, and wave spectra) during a BBE event observed by the Fast Auroral SnapshoT (FAST) satellite. The BBEs were observed at an altitude of ∼2000 km at 59°-61° invariant latitudes (ILATs) and 21 h magnetic local time (MLT). The event was observed at ∼7 min after the onset of a substorm during the main phase of the Bastille Day geomagnetic storm (minimum Dst = -301 nT) on 15 July 2000. The precipitation region of the BBEs corresponded to a localized intensification of auroral emission, lasting ∼14 min, observed by the Polar UVI images at 50°-60° geomagnetic latitudes (MLATs) and 20-21 MLTs. These results suggest that rapid particle acceleration was occurring in the inner magnetosphere associated with a storm-time substorm. The pitch angle distribution of BBEs was isotropic except for a loss cone feature around the field-aligned upward direction at a higher energy range above ∼1 keV, while field-aligned electron fluxes were larger than the perpendicular fluxes below ∼1 keV. These results imply that a higher energy part of the BBEs originated from higher altitudes in the inner magnetosphere and that a lower energy part was accelerated parallel to the local magnetic field at lower altitudes near the satellite. Intense fluctuations of electric and magnetic fields were observed during this BBE event. From these results, we discuss possible acceleration of the lower energy part of BBEs through wave-particle interaction. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JA012184

Signatures of ultra fast Kelvin waves in the equatorial middle atmosphere and ionosphere Reviewed Open Access

H. Takahashi, C. M. Wrasse, J. Fechine, D. Pancheva, M. A. Abdu, I. S. Batista, L. M. Lima, P. P. Batista, B. R. Clemesha, N. J. Schuch, K. Shiokawa, D. Gobbi, M. G. Mlynczak, J. M. Russell

GEOPHYSICAL RESEARCH LETTERS Vol. 34 ( 11 ) 2007.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

In the equatorial atmosphere, oscillations with periods of 3 to 4 days have been observed in the meteor radar zonal wind at Cariri ( 7.4 degrees S, 36.5 degrees W), in the ionospheric minimum virtual height h'F and the maximum critical frequency foF2 at Fortaleza (3.9 degrees S, 38.4 degrees W), and in the TIMED/SABER satellite temperature data in the stratosphere-mesosphere. Wavelet analyses of these time series reveal that the 3-4-day oscillation was observed for all of these data during the period from March 1 to 11, 2005. From the characteristics of the downward phase propagation ( wavelength of similar to 40 km), longitudinal and latitudinal extension, we conclude that this oscillation must be a 3.5-day Ultra Fast Kelvin (UFK) wave. This is the first report of clear evidence of propagation of a UFK wave from the stratosphere to the ionosphere. The UFK wave could have an important role in the day-to-day variability of the equatorial ionosphere evening uplift.

DOI： 10.1029/2007GL029612

Ground observation and AMIE-TIEGCM modeling of a storm-time traveling ionospheric disturbance Reviewed Open Access

Shiokawa, K, Lu, G, Otsuka, Y, Ogawa, T, Yamamoto, M, Nishitani, N, Sato, N

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 112 ( A5 ) 2007.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

This paper reports the first comparison between comprehensive observations of equatorward moving traveling ionospheric disturbance at midlatitudes and thermospheric general circulation model with high-latitude energy input based on data assimilation. A prominent traveling ionospheric disturbance (TID) was observed during the major magnetic storm of 31 March 2001. The TID propagated from north to south over Japan with phase speeds of 370-640 m/s. The assimilative mapping of ionospheric electrodynamics (AMIE) technique was used as input to the thermosphere-ionosphere-electrodynamics general circulation model (TIEGCM) to investigate generation and propagation of the observed TID. In the model, two Joule heating enhancements in the high-latitude dayside sector produced two distinct traveling atmospheric waves (TADs), which propagated to Japan in the midnight sector as enhancements in thermospheric temperature and southward wind speed. The phase speed of the TADs was much faster (∼1100 m/s) in the model, probably due to the overestimation of Joule heating in the model. The second TAD corresponds to the observed prominent TID, while signatures of the first TAD were also seen in the observed ionosonde data. The observed TID was characterized by a decrease in southward wind speed, causing a significant F-layer height decrease and a temporal enhancement of F-layer peak density. These characteristics were reproduced by the model as a rarefaction of the second TAD. The temporal enhancement of F-layer peak density was because of the vertical shear of meridional wind. The absolute value of F-layer electron density in the model was several factors smaller than that observed, probably because of the underestimation of the supply of O+ ions from the plasmasphere. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JA011772

An intense gravity wave near the mesopause region observed by a Fabry-Perot interferometer and an airglow imager Reviewed Open Access

Shiokawa, K, Suzuki, S, Otsuka, Y, Ogawa, T, Nakamura, T, Horinouchi, T

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 112 ( D7 ) 2007.4

Simultaneous ground and satellite observations of an isolated proton arc at subauroral latitudes Reviewed Open Access

K. Sakaguchi, K. Shiokawa, A. Leda, Y. Miyoshi, Y. Otsuka, T. Ogawa, M. Connors, E. F. Donovan, F. J. Rich

Journal of Geophysical Research: Space Physics Vol. 112 ( A4 ) 2007.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

We observed an isolated proton arc at the Athabasca station (MLAT: 62°N) in Canada on 5 September 2005, using a ground-based all-sky imager at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm (Hβ). This arc is similar to the detached proton arc recently observed by the IMAGE satellite [Immel et al., 2002]. The arc appeared at 0500-0640 UT (2100-2240 MLT), coincident with strong Pc 1 geomagnetic pulsations in the frequency range of the electromagnetic ion cyclotron (EMIC) wave. The isolated arc did not change its structure and intensity during the late growth and expansive phases of a small substorm that occurred at 0550 UT. From particle data obtained by the NOAA 17 satellite, we found that the isolated arc was associated with the localized enhancement of ion precipitation fluxes at an energy range of 30-80 keV at L ~ 4. Trapped ion flux enhancements (ring current ions) were also observed at two latitudinally separated regions. The localized ion precipitation was located at the outer boundary of the inner ring current ions. The DMSP F13 satellite observed signatures of an ionospheric plasma trough near the conjugate point of the arc in the Southern Hemisphere. The trough is considered to be connected to the plasmapause. These results indicate that the source region of the isolated arc was located near the plasmapause and in the ring current. We conclude that the observed isolated proton arc at subauroral latitudes was caused by the EMIC waves, which were generated near the plasmapause and resonantly scattered the ring current protons into the loss cone. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JA012135

Estimating drift velocity of polar cap patches with all-sky airglow imager at Resolute Bay, Canada Reviewed

A concentric gravity wave structure in the mesospheric airglow images Reviewed Open Access

Suzuki, S, Shiokawa, K, Otsuka, Y, Ogawa, T, Nakamura, K, Nakamura, T

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 112 ( 2 ) 2007.1

Gravity wave momentum flux in the upper mesosphere derived from OH airglow imaging measurements Reviewed Open Access

Suzuki Shin, Shiokawa Kazuo, Otsuka Yuichi, Ogawa Tadahiko, Kubota Minoru, Tsutsumi Masaki, Nakamura Takuji, Fritts David C.

EARTH PLANETS AND SPACE Vol. 59 ( 5 ) page： 421 - 428 2007

Simultaneous DMSP, all-sky camera, and IMAGE FUV observations of the brightening are at a substorm pseudo-breakup Reviewed Open Access

Yago K., Shiokawa K., Yumoto K., Baishev D. G., Solovyev S. I., Rich F. J.

EARTH PLANETS AND SPACE Vol. 59 ( 1 ) page： 45 - 49 2007

Development of airglow temperature photometers with cooled-CCD detectors Reviewed Open Access

Shiokawa K., Otsuka Y., Suzuki S., Katoh T., Katohl Y., Satoh M., Ogawa T., Takahashi H., Gobbli D., Nakamura T., Williams B. P., She C.-Y., Taguchi M., Shimomai T.

EARTH PLANETS AND SPACE Vol. 59 ( 6 ) page： 585 - 599 2007

The ionospheric response in the Brazilian sector during the super geomagnetic storm on 20 November 2003 Reviewed Open Access

Becker-Guedes F., Sahai Y., Fagundes P. R., Espinoza E. S., Pillat V. G., Lima W. L. C., Basu Su., Basu Sa., Otsuka Y., Shiokawa K., MacKenzie E. M., Pi X., Bittencourt J. A.

ANNALES GEOPHYSICAE Vol. 25 ( 4 ) page： 863 - 873 2007

Summer-winter hemispheric asymmetry of sudden increase in ionospheric total electron content induced by solar flares: A role of O/N2 ratio Reviewed Open Access

T. Tsugawa, T. Sadakane, J. Sato, Y. Otsuka, T. Ogawa, K. Shiokawa, A. Saito

Journal of Geophysical Research A: Space Physics Vol. 111 ( A11 ) 2006.11

A fast-propagating, large-scale atmospheric gravity wave observed in the WAVE2004 campaign Reviewed Open Access

Minoru Kubota, Seiji Kawamura, Makoto Abo, Yoshiko Koizumi, Yasuhiro Murayama, Miho Yamamori, Kazuo Shiokawa, Yuichi Otsuka, Michihiro Uchiumi, Kiyoshi Igarashi, Takumi Abe, Koh-Ichiro Oyama, Naomoto Iwagami

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 111 ( D21 ) page： D21110 - D21110 2006.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

The Waves in Airglow Campaign in 2004 (WAVE2004), which aimed to elucidate the formation process of waves in airglow structures from both dynamical and chemical perspectives, was conducted using rocket-borne and ground-based instruments in Japan on 17 January 2004. In this experiment, we observed a large-scale atmospheric gravity wave (AGW), which appeared in both the vertical profiles of sodium density obtained by a Na lidar and the horizontal distributions of airglow emission obtained by an all-sky imager (ASI). Vertical propagation of the AGW accompanied by a shortening of its vertical wavelength was clearly visualized using the Na lidar data. The horizontal wavelength, horizontal phase velocity, period, and propagation direction of the AGW were estimated from the ASI data as 673-774 km, 107-122 m/s, similar to 1.75 hours, and north-northeastward, respectively. Using these parameters and the MF radar wind, vertical wavelengths of the wave were calculated from the dispersion relation of gravity waves. The calculated vertical wavelengths were comparable at altitudes of 85.5 km and 93.25 km to those estimated from the variation of the sodium density. Using a simple ray tracing technique, the AGW was traced back to the southern edge of the distorted jet stream near tropopause. This result strongly suggests that an unstable baroclinic wave associated with ageostrophic motions in the jet stream was the wave source of the large-scale AGW observed in the WAVE2004.

DOI： 10.1029/2005JD006788

B153 地上からの光学・電波による中間圏重力波の観測(スペシャルセッション「高解像度気候モデルによる中層大気研究の可能性」) Reviewed Open Access

中村卓司, 塩川和夫, 堤雅基, 川原琢哉

大会講演予講集 Vol. 90 page： 100 2006.9

Hosokawa, K, Shiokawa, K, Otsuka, Y, Nakajima, A, Ogawa, T, Kelly, JD

GEOPHYSICAL RESEARCH LETTERS Vol. 33 ( 15 ) 2006.8

Ionospheric disturbances over Indonesia and their possible association with atmospheric gravity waves from the troposphere Reviewed Open Access

Ogawa Tadahiko, Otsuka Yuichi, Shiokawa Kazuo, Saito Akinori, Nishioka Michi

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN Vol. 84A page： 327 - 342 2006.7

A multi-instrument measurement of a mesospheric front-like structure at the equator Reviewed Open Access

Shiokawa Kazuo, Suzuki Shin, Otsuka Yuichi, Ogawa Tadahiko, Nakamura Takuji, Mlynczak Martin G., Russell James M. III

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN Vol. 84A page： 305 - 316 2006.7

Equatorial ionospheric scintillations and zonal irregularity drifts observed with closely-spaced GPS receivers in Indonesia Reviewed Open Access

Otsuka Yuichi, Shiokawa Kazuo, Ogawa Tadahiko

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN Vol. 84A page： 343 - 351 2006.7

Quasiperiodic southward moving waves in 630-nm airglow images in the equatorial thermosphere Reviewed Open Access

Shiokawa, K, Otsuka, Y, Ogawa, T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 111 ( A6 ) 2006.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

We report quasiperiodic southward moving waves, which are commonly observed in the 01 630-nm airglow images (emission altitudes of 200-300 km) near the equator, in 2-year airglow observations at Kototabang, Indonesia (0.2°S, 100.3°E, geomagnetic latitude of -10.4°). The waves have predominantly east-west phase fronts and repeatedly propagate southward with a velocity of 310 ± 110 m/s and a period of 40 ± 15 min. They are frequently observed in May-July with an occurrence rate of 53% and are also observed in other seasons with occurrences of ∼20%. The waves are observed in and to the south (geomagnetically poleward) of the equatorial ionospheric anomaly, which is identified as an airglow enhancement region moving gradually to lower geomagnetic latitudes at the premidnight local times. We suggest that gravity waves in the lower thermosphere below ∼300 km are a plausible cause of the observed quasiperiodic waves in the airglow images. Copyright 2006 by the American Geophysical Union.

DOI： 10.1029/2005JA011406

Geomagnetic conjugate observations of large-scale traveling ionospheric disturbances using GPS networks in Japan and Australia Reviewed Open Access

Takuya Tsugawa, Kazuo Shiokawa, Yuichi Otsuka, Tadahiko Ogawa, Akinori Saito, Michi Nishioka

Journal of Geophysical Research: Space Physics Vol. 111 ( A2 ) 2006.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

The geomagnetic conjugacy of large-scale traveling ionospheric disturbances (LSTIDs) was studied using total electron content (TEC) data derived from GPS networks in Japan and Australia. The number of simultaneous occurrences of LSTIDs within ±1 hour in both hemispheres was 5 out of 20 (21) events in Japan (Australia) when Kp ≥ 5- and 0 out of 15 (10) when Kp ≤ 4+. As for the LSTIDs observed simultaneously in both hemispheres, the propagation velocities of equatorward LSTID were comparable between the two hemispheres, with differences of 10-40%. The crossing times at 30° geomagnetic latitude of the simultaneous LSTIDs over Japan and Australia were also different by several tens of minutes for all five events. These observational results indicate that the LSTIDs observed almost simultaneously in both hemispheres are not connected electromagnetically through the geomagnetic field but are generated by atmospheric gravity waves propagating to the equator independently in the two hemispheres. Copyright 2006 by the American Geophysical Union.

DOI： 10.1029/2005JA011300

ERG - A small-satellite mission to investigate the dynamics of the inner magnetosphere Reviewed

Shiokawa K., Seki K., Miyoshi Y., Ieda A., Ono T., Iizima M., Nagatsuma T., Obara T., Takashima T., Asamura K., Kasaba Y., Matsuoka A., Saito Y., Saito H., Hirahara M., Tonegawa Y., Toyama F., Tanaka M., Nose M., Kasahara Y., Yumoto K., Kawano H., Yoshikawa A., Ebihara Y., Yukimatsu A., Sato N., Watanabe S.

MAGNETOSPHERIC DYNAMICS AND THE INTERNATIONAL LIVING WITH A STAR PROGRAM Vol. 38 ( 8 ) page： 1861-1869 2006

Signatures of 3-6 day planetary waves in the equatorial mesosphere and ionosphere Reviewed Open Access

Takahashi H., Wrasse C. M., Pancheva D., Abdu M. A., Batista I. S., Lima L. M., Batista P. P., Clemesha B. R., Shiokawa K.

ANNALES GEOPHYSICAE Vol. 24 ( 12 ) page： 3343 - 3350 2006

GPS detection of total electron content variations over Indonesia and Thailand following the 26 December 2004 earthquake Reviewed Open Access

Otsuka Y, Kotake N, Tsugawa T, Shiokawa K, Ogawa T, Effendy, Saito S, Kawamura M, Maruyama T, Hemmakorn N, Komolmis T

EARTH PLANETS AND SPACE Vol. 58 ( 2 ) page： 159 - 165 2006

the Inner Magnetosphere Subgroup in the Society of Geomagnetism and Earth, Planetary and Space Sciences ERG -A small-satellite mission to investigate the dynamics of the inner magnetosphere Reviewed

塩川和夫

Adv. Space Res 38(8) page： 1861 - 1869 2006

Effects of the major geomagnetic storms of October 2003 on the equatorial and low-latitude F region in two longitudinal sectors Reviewed Open Access

Y Sahai, PR Fagundes, F Becker-Guedes, MJA Bolzan, Abalde, JR, VG Pillat, R de Jesus, WLC Lima, G Crowley, K Shiokawa, JW MacDougall, HT Lan, K Igarashi, JA Bittencourt

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 110 ( A12 ) 2005.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

The intense modifications in the ionosphere-thermosphere system in the equatorial and low-latitude regions associated with the dynamic and electrodynamic coupling from high to low latitudes and chemical changes during geomagnetic storms are important space weather issues. In the second half of October 2003, the intense solar activity resulted in one intense and two major geomagnetic storms on 29 and 30 October. In this paper we present and discuss the ionospheric sounding observations carried out from Palmas and Sao Jose dos Campos, Brazil (the Brazilian sector), and Ho Chi Minh City, Vietnam, and Okinawa, Japan (the East Asian sector), during these storms. The two sectors are separated by about 12 hours in local time (so while one sector is in daytime, the other one is in nighttime) and provide valuable information related to the storm-time longitudinal differences. Copious storm-time changes were observed in both sectors. It should be pointed out that the two longitudinal sectors investigated in the present study clearly show the global nature of the storm-time effects. However, the responses to the storm-time effects are also associated with the local time in the two sectors. The present investigations show that there are both similarities and differences in the storm-time response in the two sectors. During the storm main phases, with sharp decreases of the Dst index, both sectors showed (dusk or dawn periods) fast uplifting of the F layer associated with magnetospheric electric field penetration. Although in the East Asian sector, Ho Chi Minh City and Okinawa are located fairly close in longitude, with only 2 hour difference in local lime, on occasions the storm-time responses have been very different. Some differences in the latitudinal response of the F region were also observed in the two sectors. Both positive and negative storm phases have been observed at all the four stations. A comparison of the ionospheric parameters obtained from the TIMEGCM model runs and the observed ionospheric parameters at the four stations shows a reasonable agreement during the quiet periods. During the geomagnetic disturbance period, when there were sharp decreases in Dst, some of the observed rapid uplifts of the F region peak heights are not reproduced by the model results. Also, sometimes the model foF2 results differ considerably from the observed foF2 variations. The period investigated represents an extreme storm situation for validation of the model and points to ways in which the model might be improved in the future.

DOI： 10.1029/2004JA010999

Ground and satellite observations of substorm onset arcs Reviewed Open Access

K Shiokawa, K Yago, K Yumoto, DG Baishev, SI Solovyev, FJ Rich, SB Mende

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 110 ( A12 ) 2005.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

[1] Auroral features and associated particles and fields are investigated for a sequence of substorm onsets observed at similar to 1900 MLT on 24 October 2000. During a 30-min interval at 1020 - 1050 UT, we identified three Pi 2 wave packets with positive H enhancements at midlatitudes and associated auroral brightenings in auroral images obtained by a ground all-sky camera and the IMAGE FUV imager. The DMSP F15 satellite crossed brightening arcs during the third Pi 2 pulsation in the field-of-view of the ground camera at Tixie (66.0 degrees MLAT), Russia. The crossing was 1 - 2 hours duskside of the main onset local time. The brightening arcs were located in the region 1 upward field-aligned current system. The most equatorward arc, which brightened just after the second Pi 2 pulsation, was at the equatorward boundary of the region 1 current and in the sunward convection region. The arcs corresponded to inverted-V accelerated electrons with energies of similar to 10 keV. On the basis of these simultaneous ground-satellite measurements, we discuss substorm onset models of reconnection/ flow braking and near-Earth plasma sheet instabilities.

DOI： 10.1029/2005JA011281

Decrease in B-z prior to the dipolarization in the near-Earth plasma sheet Reviewed Open Access

K Shiokawa, Y Miyashita, Shinohara, I, A Matsuoka

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 110 ( A9 ) 2005.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

[1] We examine in detail the rapid decrease in B-z just before dipolarizations observed by the Geotail satellite in the near-Earth plasma sheet at (X-GSM, Y-GSM) = (-8.3 R-E, - 5.1 R-E). The observations were made using high-time-resolution data from a fluxgate magnetometer (16-Hz sample), a search-coil magnetometer ( 128 Hz), and an electric field antenna ( 64 Hz). Two dipolarizations were observed during a short time interval of 2 min. The magnetic Bz component suddenly decreased 2 - 4 s prior to the dipolarization. Characteristic waves with frequencies of 5 - 20 Hz and amplitudes of 1 - 3 mV m(-1) and 5 - 15 nT s(-1) were observed in the electric and magnetic field data at the time of the sudden decreases in B-z. We discuss two possible causes of the sudden decreases in B-z prior to the dipolarizations: ( 1) passage of a field-aligned line current associated with the substorm current wedge and ( 2) explosive growth phase and subsequent disruption of the tail current caused by the observed characteristic field oscillations.

DOI： 10.1029/2005JA011144

Observations of equatorial plasma bubbles using broadcast VHF radio waves Reviewed Open Access

Nakata, H, Nagashima, I, Sakata, K, Otsuka, Y, Akaike, Y, Takano, T, Shimakura, S, Shiokawa, K, Ogawa, T

GEOPHYSICAL RESEARCH LETTERS Vol. 32 ( 17 ) page： 1 - 4 2005.9

Language：English Publishing type：Research paper (scientific journal)

The propagation of VHF radio waves affected by field-aligned irregularities within equatorial plasma bubbles is examined. Continuous observation of VHF radio waves at Tateyama, Japan, shows that broadcast radio waves transmitted from Southeast Asia propagate to Japan. Using a ray-tracing calculation combined with a model of scattering by field-aligned irregularities, we determined scatter points suitable for the reception of these radio waves. The results of the calculation show that radio waves transmitted from the Philippines can propagate to Japan owing to field-aligned irregularities within equatorial plasma bubbles located west of Japan. Comparing with all-sky imager data observed at Sata, Japan, we found that the radio waves are received at Tateyama when the plasma bubbles are observed at Sala. The results of this study show that the reception of these radio waves is closely correlated with the equatorial plasma bubbles. Copyright 2005 by the American Geophysical Union.

DOI： 10.1029/2005GL023243

Development of the Virtual Earth's Magnetosphere System (VEMS) Reviewed

Murata Ken T., Yamamoto Kazunori, Matsuoka Daisuke, Kimura Eizen, Matsumoto Hiroshi, Okada Masaki, Mukai Toshifumi, Sigwarth John B., Fujita Shigeru, Tanaka Takashi, Yumoto Kiyohumi, Ogino Tatsuki, Shiokawa Kazuo, Tsyganenko Nikolai A., Green James L., Nagai Tsugunobu

Advances in polar upper atmosphere research Vol. 19 page： 135 - 151 2005.8

Language：English Publishing type：Research paper (scientific journal) Publisher：National Institute of Polar Research

We have constructed a new research environment for geo-space science based on 3-D visualization tool and network database; Virtual Earth's Magnetosphere System (VEMS). With an interactive research environment researchers can visually understand structures of the Earth's magnetosphere using VEMS. On the VEMS, computer simulation results and observation data are simultaneously visualized, having a potential to data assimilation for geo-space studies in the future. Since the VEMS deals with time-dependent data, it also helps researchers to study dynamics of the Earth's magnetosphere. We found that immersive data analyses are possible using the VEMS on a virtual reality system.

Magnetic field fluctuations during substorm-associated dipolarizations in the nightside plasma sheet around X=-10 R-E Reviewed Open Access

K Shiokawa, Shinohara, I, T Mukai, H Hayakawa, CZ Cheng

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 110 ( A5 ) 2005.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Using high-time-resolution data for the magnetic field (1/16 s), plasma moment (12 s), and electric field (3 s) obtained by Geotail, we have investigated various characteristics of magnetic field fluctuations for 21 events of substorm-associated near-Earth dipolarization at X-GSM = -8 similar to -11 R-E and vertical bar Y(GSM)vertical bar < 5 R-E. The dipolarizations were always accompanied by fluctuations of the magnetic field. The amplitude of the fluctuations tends to be larger for smaller ambient magnetic field. For several events we found that magnetic field elevation angles show rapid decrease prior to the rapid increase (features like explosive growth phase). Compressional fluctuations of magnetic field intensity B show characteristic spikes of a sudden decrease and increase with a timescale of seconds. For quite a few cases the fluctuations are accompanied by enhancements of earthward plasma velocity. The spectral shape of the B fluctuations had a steeper slope (f(-2.7)) at higher frequency range at 1.0-0.2 Hz than at 0.01-0.2 Hz (f(-2.0)) for the events closer to the cross-tail current sheet (smaller ambient-B region). We found that the steeper slope extends to lower frequency range below 0.2 Hz for the events away from the current sheet (larger ambient-B region). This fact may suggest transition from three-dimensional to two-dimensional turbulence from smaller B to larger B region. We also investigated correlation of fluctuations in plasma velocity and magnetic field for waves with periods around 60 s. The correlations were rather weak, suggesting that non-MHD plasma processes are going on. For these waves, the magnetic and plasma pressure variations were clearly antiphase.

DOI： 10.1029/2004JA010378

Geomagnetic conjugate observation of nighttime medium-scale and large-scale traveling ionospheric disturbances: FRONT3 campaign Reviewed Open Access

Shiokawa K, Otsuka Y, Tsugawa T, Ogawa T, Saito A, Ohshima K, Kubota M, Maruyama T, Nakamura T, Yamamoto M, Wilkinson P

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 110 ( A5 ) 2005.5

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Space Physics

The third FRONT (F-region Radio and Optical measurement of Nighttime TID) campaign was carried out during the new-moon period of May-June 2003, in order to investigate the geomagnetic conjugacy of medium-scale and large-scale traveling ionospheric disturbances (MSTIDs/LSTIDs) at midlatitudes. Seven all-sky airglow imagers were operated in Japan and Australia. For almost all clear-sky nights, we observed MSTIDs in the 630-nm airglow images with horizontal wavelengths of 100-400 km propagating southwestward in Japan and northwestward in Australia. All of them show a one-to-one correspondence of wave structures between the Northern and Southern Hemispheres, indicating strong electrodynamic coupling between the two hemispheres through the geomagnetic field line. We also found that airglow intensity variations with a timescale longer than that of MSTIDs often show a good correlation between the two hemispheres. On 28 May, we succeeded in detecting an equatorward propagating LSTID (spatial scale ∼1000 km) as airglow enhancements at the conjugate stations. The airglow peak of the LSTID in the Northern Hemisphere was ∼20 min earlier than that in the Southern Hemisphere, indicating that the observed LSTID is caused by a wave in the neutral atmosphere rather than by an electric field structure. Copyright 2005 by the American Geophysical Union.

DOI： 10.1029/2004JA010845

Low-latitude auroras observed in Japan: 1999-2004 Reviewed Open Access

Shiokawa K, Ogawa T, Kamide Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 110 ( A5 ) 2005.5

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

[1] From routine observations by means of highly sensitive all-sky cameras and tilting-filter photometers, a total of 20 low-latitude aurora events in Japan were identified during the high solar activity period of 1999 - 2004. This indicates that the invisible-level auroras appear rather frequently in the northern sky of Japan during magnetic storms. These auroras are characterized by an enhancement in red (630.0 nm) emissions in the northern sky during magnetic storms, probably at geomagnetic latitudes higher than &SIM; 40 - 50&DEG;. We show examples of stable auroral red (SAR) arcs, which are typically observed during the recovery phase of storms. We also found several red aurora events that occurred at the initial phase of magnetic storms. Intensifications as well as equatorward motion of the auroras were observed in association with storm time substorms. Green line emissions (557.7 nm) were often enhanced (&SIM; 1 kR) not only in the northern sky but also in the whole sky. Some auroras show weak enhancements (&SIM; 10 R) of N-2(+) 1N (427.8 nm) in the northern sky in the morning hours. We discuss possible causes of these emissions in light of magnetospheric disturbances and thermospheric dynamics.

DOI： 10.1029/2004JA010706

館山におけるVHF帯電波受信のプラズマバブル緯度依存性について Reviewed

P253 中間圏の大気光画像中に現れた湾曲波面を持つ大気重力波の構造 Reviewed Open Access

鈴木臣, 塩川和夫, 中村健治, 大塚雄一, 小川忠彦, 中村卓司

大会講演予講集 Vol. 87 page： 374 2005.4

坂田健一郎, 中田裕之, 鷹野敏明, 島倉信, 大塚雄一, 塩川和夫, 小川忠彦

大気電気研究 Vol. 66 page： 63 - 64 2005.3

Auroral particles associated with a substorm brightening arc Reviewed Open Access

K Yago, K Shiokawa, K Hayashi, K Yumoto

GEOPHYSICAL RESEARCH LETTERS Vol. 32 ( 6 ) page： 1 - 4 2005.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We investigated the characteristics of auroral precipitating particles associated with a brightened arc at a pseudo-substorm, using auroral images of a high-time resolution (0.25 s) all-sky TV camera, particle data from the DMSP F10 spacecraft, and high-latitude magnetograms. The arc brightening occurred at 0407 UT ( similar to 20 MLT) on December 30, 1994, at Fort Smith ( 67 MLAT), Canada, coincident with high-latitude Pi 2 magnetic pulsations. The brightening appeared without expansion (pseudo-breakup), and Fort Smith was located duskside of the main onset region. From the simultaneous DMSP particle data, the brightened arc is found to correspond to an electron inverted-V structure near the equatorward edge of the electron precipitation region, suggesting the pseudo-breakup of the auroral substorm occurred in the inner part of the plasma sheet.

DOI： 10.1029/2004GL021894

Relationship between propagation direction of gravity waves in OH and OI airglow images and VHF radar echo occurrence during the SEEK-2 campaign Reviewed Open Access

Onoma F, Otsuka Y, Shiokawa K, Ogawa T, Yamamoto M, Fukao S, Saito S

ANNALES GEOPHYSICAE Vol. 23 ( 7 ) page： 2385 - 2390 2005

Geoeffectiveness of shocks in populating the radiation belts Reviewed

JB Blake, PL Slocum, JE Mazur, MD Looper, RS Selesnick, K Shiokawa

Multiscale Coupling of Sun-Earth Processes page： 125 - 133 2005

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ELSEVIER SCIENCE BV

On 24 March 1991, ions and electrons with energies of 10s of MeV were observed by CRRES to be injected into the Earth's magnetosphere. The injection created a stable new radiation belt that persisted for years. Later in the decade, several geomagnetic storms and associated energetic solar particle events led to new radiation belts, but none with comparable stability until two injections occurred in November 2001 that lasted for two years. Using data from SAMPEX, Polar, 1997-068, and the 210 Magnetic Meridian Chain, we examine observations of storms that lead to new long-lasting belts. We find that stable belts arise after a deep injection into the slot region (L similar to 2.5). Associated with these injections is an unusually rapid rise in the magnetic field impulse as seen by ground-based magnetometers.

DOI： 10.1016/B978-044451881-1/50010-1

Spatial relationship of equatorial plasma bubbles and field-aligned irregularities observed with an all-sky airglow imager and the Equatorial Atmosphere Radar Reviewed

The first coordinated observations of mid-latitude E-region quasi-periodic radar echoes and lower thermospheric 557.7-nm airglow Reviewed Open Access

Ogawa, T, Otsuka, Y, Onoma, F, Shiokawa, K, Yamamoto, M

ANNALES GEOPHYSICAE Vol. 23 ( 7 ) page： 2391 - 2399 2005

Simultaneous ground- and satellite-based airglow observations of geomagnetic conjugate plasma bubbles in the equatorial anomaly Reviewed Open Access

Ogawa T, Sagawa E, Otsuka Y, Shiokawa K, Immel TI, Mende SB, Wilkinson P

EARTH PLANETS AND SPACE Vol. 57 ( 5 ) page： 385 - 392 2005

Otsuka Y, Shiokawa K, Ogawa T, Yokoyama T, Yamamoto M, Fukao S

GEOPHYSICAL RESEARCH LETTERS Vol. 31 ( 20 ) page： L20802 2004.10

中間圏の大気光画像中に現れた湾曲波面を持つ大気重力波の構造 Reviewed Open Access

鈴木臣, 塩川和夫, 中村健治, 大塚雄一, 小川忠彦, 中村卓司

大会講演予講集 Vol. 86 page： . 2004.10

Cosmic Ray and Riometer Observations in Associated with Thunderstorm at Brazilian Geomagnetic Anomaly Region Reviewed

MAKITA Kazuo, TORII Tatuo, HOSHINO Mituo, NISHINO Masonori, SHIOKAWA Kazuo, SCHUCH Nelson Jorge

Bulletin of science and engineering, Takushoku University Vol. 9 ( 2 ) page： 37 - 42 2004.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Takushoku University

A field mill and a cosmic-ray detector have been newly installed at Brazilian geomagnetic anomaly region. We have compared 38.2 MHz riometer with these data during strong thunderstorm period. Although no clear relationship have been recognized yet between electric field and the fluctuation of cosmic-ray intensity, however a good relationship was found between electric field and 38.2 MHz intensity. This result may suggest that 38.2 MHz radio wave was excited by acceleration of particles under the thunderstorm electric field.

Statistical characteristics of gravity waves observed by an all-sky imager at Darwin, Australia Reviewed Open Access

Shin Suzuki, K. Shiokawa, Y. Otsuka, T. Ogawa, P. Wilkinson

Journal of Geophysical Research D: Atmospheres Vol. 109 ( D20 ) page： D20 - S07 2004.8

Language：English Publishing type：Research paper (scientific journal)

An all-sky airglow imager with a cooled charge-coupled device camera in place at Darwin (12.4°S, 131.0°E), Australia, since October 2001 has been used to obtain two-dimensional gravity wave images in the mesopause region. Using airglow images of the OI (557.7 nm, emission altitude ∼96 km) and OH band (720-910 nm, ∼86 km) emissions obtained for October 2001 to August 2002, we investigated the wavelengths, phase velocities, and propagation directions of gravity waves. Wave occurrence in OH images (60-90%) is higher than in OI images (30-70%) for all seasons. The waves have wavelengths of less than 90 km (peak: 30-50 km) and phase velocities ofless than 90 m/s (peak: 30-60 m /s). Most of the waves propagate in the meridional direction, and the directionality strongly depends on the season. In winter, waves propagate both poleward and equatorward, while in summer almost all waves propagate poleward. An examination of airglow-imaging statistics at Adelaide (35°S, 138°E), Australia, obtained by Walterscheid et al. [1999], leads us to conclude that this clear directionality is caused by the location of the wave sources and by the wave ducting processes
that is, poleward waves in summer come from an equatorial convective source through a thermal duct structure. The effect of wind filtering on the waves is also discussed for zonal wave propagation. Copyright 2004 by the American Geophysical Union.

DOI： 10.1029/2003JD004336

Geomagnetic conjugate observations of medium-scale traveling ionospheric disturbances at midlatitude using all-sky airglow imagers Reviewed

Y Otsuka, K Shiokawa, T Ogawa, P Wilkinson

GEOPHYSICAL RESEARCH LETTERS Vol. 31 ( 15 ) 2004.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report for the first time simultaneous observations of medium-scale traveling ionospheric disturbances (MSTIDs) at geomagnetic conjugate points in both hemispheres, using two all-sky airglow imagers at midlatitudes. A 630-nm all-sky CCD imager at Sata, Japan, detected MSTIDs with a wavefront elongated from NW to SE on the night of August 9, 2002. During this event, MSTIDs with a wavefront elongated from SW to NE were observed at the geomagnetic conjugate point, Darwin, Australia. To investigate geomagnetic conjugacy of the MSTID structures, the Darwin images were mapped The MSTID structures mapped from Darwin to its magnetic conjugate points along the geomagnetic field lines ( B) coincide closely with those in the Sata images. This result suggests that polarization electric field (E-p) plays an important role in the generation of MSTIDs. E-p maps along B and moves the F region plasma upward or downward by E x B drifts, causing plasma density perturbations with structures mirrored in the northern and southern hemispheres.

DOI： 10.1029/2004GL020262

Comparison of OH rotational temperatures measured by the spectral airglow temperature imager (SATI) and by a tilting-filter photometer Reviewed

内部磁気圏ミッションの提案

塩川和夫, 関加奈子, 三好由純, 小原隆博, 小野高幸

第4回宇宙科学シンポジウム proceeding page： 349 - 352 2004.8

Shiokawa, K, Otsuka, Y, Ogawa, T, Takahashi, H, Nakamura, T, Shimomai, T

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 66 ( 11 ) page： 891 - 897 2004.7

大気光画像データを用いた中間圏重力波の運動量フラックスの導出 Reviewed Open Access

鈴木臣, 塩川和夫, 大塚雄一, 小川忠彦, 中村卓司, FRITTS D. C.

大会講演予講集 Vol. 85 page： . 2004.5

Simultaneous mesosphere/lower thermosphere and thermospheric F region observations during geomagnetic storms Reviewed Open Access

Balan, N, Kawamura, S, Nakamura, T, Yamamoto, M, Fukao, S, Igarashi, K, Maruyama, T, Shiokawa, K, Otsuka, Y, Ogawa, T, Alleyne, H, Watanabe, S, Murayama, Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 109 ( A4 ) 2004.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

Simultaneous mesosphere/lower thermosphere (MLT) and thermospheric F region observations made during geomagnetic storms are presented using the MU radar (35°N, 136°E) in alternate meteor and incoherent scatter (IS) modes, MF radar (45°N, 136°E), optical mesosphere thermosphere imagers (OMTI) (35°N, 136°E) and over 1000 GPS receivers in Japan. The observations were made during one of the MTEC-S (mesospherethermosphere experiments for coupling studies) campaigns conducted during 23 March to 2 April 2001 when a major storm with Dst reaching -358 nT and a moderate storm with Dst reaching -112 nT occurred and solar activity varied from high to very high (F10.7 = 220 to 270). The campaign has provided zonal and meridional wind velocities at MLT altitudes (80-95 km) over the MU and MF radars
meridional wind velocity in the upper thermosphere (220-450 km) and ionospheric electron density (150-600 km), peak height and plasma drift velocity over the MU radar
all-sky airglow intensities at 557.7 nm, 630.0 nm, and 777.4 nm wavelengths over the MU radar location
and vertical GPS-TEC all over Japan. Study of the data indicates that following the major storm, the meridional wind in the upper thermosphere over the MU radar (35°N) becomes weak (less poleward) during daytime and its diurnal amplitude reduces. The winds and tides at MLT altitudes show changes during both nonstorm times and storm times, but this study is not able to confirm any statistically significant changes related to the storms. In the ionosphere, following the onset of the major morning storm, the electron density increases at altitudes near and above the ionospheric peak, which after about 5 hours is followed by large increase in density at all altitudes above about 200 km. On the following night, though the density is generally low, there is a large increase in density in the bottomside for about 3 hours centered at 0230 LT. During this time, a rare intense optical activity has occurred at all wavelengths (557.7 nm, 630 nm, and 777.4 nm) over the low midlatitude location (35°N), and an associated large-scale traveling ionospheric disturbance (LSTID) has propagated from north to south at F region altitudes. Copyright 2004 by the American Geophysical Union.

DOI： 10.1029/2003JA009982

VHF海外放送電波の伝搬とプラズマバブルとの関連 Reviewed

長嶋郁生, 中田裕之, 大塚雄一, 鷹野敏明, 坂井来人, 塩川和夫, 小川忠彦

大気電気研究 Vol. 64 page： 82 - 83 2004.3

Optical Observation at Okinawa Reviewed

MAKITA Kazuo, HOSHINO Mituo, MASUDA Yoshihisa, SHIOKAWA Kazuo

Bulletin of science and engineering, Takushoku University Vol. 9 ( 1 ) page： 19 - 26 2004.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Takushoku University

CCD imager and Photometer were installed at CRL Oogimi ionospheric station at Okinawa (26.7 N, 128 E) in order to compare optical data obtained at INPE Southern Space Observatory, Brazil (29.6 S, 306 E). These two observatories are nearly opposite side of earth. From Okinawa optical data, 630nm enhancement was observed at pre-morning sector (03-05 LT). The peak luminosity of 630nm was about 300-400 R and no clear enhancement in 557.7nm. These phenomena are very similar to the optical data obtained at Brazilian observatory. It suggests that the pre-morning enhancement of 630nm observed here must be general phenomena in low latitude region. We are now examining the relationship between ionospheric electron density and those 600nm enhancement.

Comparison of winds measured by MU radar and Fabry-Perot interferometer and effect of OI5577 airglow height variations Reviewed

J Fujii, T Nakamura, T Tsuda, K Shiokawa

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 66 ( 6-9 ) page： 573 - 583 2004

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

We have compared wind velocities around mesopause height measured by the middle and upper atmosphere (MU) radar (meteor mode) and O1 (5577) airglow observation by an Fabry-Perot Interferometer (FPI), at Shigaraki (34.8degreesN, 136.1degreesE), Japan, on November 13/14, 1999. When we assume the airglow height is constant throughout the night, it was difficult to find a single height exhibiting small r.m.s. differences between the two methods for both eastward and northward wind velocities. However, in the case we introduce a time variation of the airglow height due to a large-scale gravity wave activity, we have found very small r.m.s. wind difference: The assumptions are of the airglow height variation with an amplitude of 1.5 km, a period of 5.7 h and a linear trend of -0.19 km/h having the average height of 92.8 km. Further analysis of time and height variations of the winds and diffusion coefficients measured by the MU radar indicated that a gravity wave with a very similar structure predicted in the above comparison between the FPI and meteor winds has been detected as a dominant wave component. Thus, we conclude that the existence of a gravity wave which can change the airglow height will lead to differences in wind velocities observed with FPI and radar techniques. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jastp.2004.01.010

Understanding the “SEKKI” phenomena in Japanese historical literatures based on the modern science of low-latitude aurora Open Access

Time evolution of high-altitude plasma bubbles imaged at geomagnetic conjugate points Reviewed Open Access

Shiokawa K, Otsuka Y, Ogawa T, Wilkinson P

ANNALES GEOPHYSICAE Vol. 22 ( 9 ) page： 3137 - 3143 2004

Atmospheric density and pressure inferred from the meteor diffusion coefficient and airglow O(2)b temperature in the MLT region Reviewed Open Access

H Takahashi, T Nakamura, K Shiokawa, T Tsuda, LM Lima, D Gobbi

EARTH PLANETS AND SPACE Vol. 56 ( 2 ) page： 249 - 258 2004

Language：English Publishing type：Research paper (scientific journal) Publisher：TERRA SCIENTIFIC PUBL CO

Atmospheric density and pressure in the upper mesosphere-lower thermosphere (MLT) region, around 90 km, are inferred from the meteor trail ambipolar diffusion coefficients, D, and simultaneously observed airglow O(2)b rotational temperatures. For the present study simultaneous observation data from the meteor radar and SATI imaging spectrometer taken at Shigaraki MU radar observatory (34.9degreesN, 136.1degreesE) were used. From the 18 winter nights of data, it is observed that in most of the cases nocturnal variation of the O-2 temperature has a good correlation with D at 90 to 92 km. The inferred densities at 90 km showed a negative correlation with temperature variation, suggesting a constant pressure process. The O-2 emission intensity shows a good correlation with the temperature, and negative correlation with the density variation. The OH rotational temperature and D at 87 km also showed similar results to the case of the O-2 temperature.

DOI： 10.1186/BF03353407

Nakazawa Yoh, Okada Toshimi, Shiokawa Kazuo

Earth, Planets and Space Vol. 56 ( 12 ) page： e41 - e44 2004

Language：English Publishing type：Research paper (scientific journal) Publisher：Society of Geomagnetism and Earth, Planetary and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan , The Geodetic Society of Japan , The Japanese Society for Planetary Sciences

“SEKKI” phenomena often appear in the Japanese historical literatures as distinct red emission in the nocturnal sky. The Japanese word “SEKKI” means the red atmosphere. We compile 16 events of SEKKI for 12-19th centuries in the literatures. In order to understand the SEKKI phenomena, we compared 2 events of SEKKI on February 21, 1204, and September 17, 1770, with the characteristics of low-latitude auroras studied recently by modern scientific methods. We conclude that these historical SEKKI phenomena are probably giant low-latitude auroras.

DOI： 10.1186/bf03353323

Thermospheric wind during a storm-time large-scale traveling ionospheric disturbance Reviewed Open Access

K Shiokawa, Y Otsuka, T Ogawa, S Kawamura, M Yamamoto, S Fukao, T Nakamura, T Tsuda, N Balan, K Igarashi, G Lu, A Saito, K Yumoto

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 108 ( A12 ) 2003.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

[1] A prominent large-scale traveling ionospheric disturbance (LSTID) was observed in Japan during the major magnetic storm (Dst similar to -358 nT) of 31 March 2001. It was detected as enhancements of the 630-nm airglow and foF2, GPS-TEC variations, and a decrease in F-layer virtual height at 1700 - 1900 UT (0200 - 0400 LT). It moved equatorward with a speed of similar to600 m/s. The decrease in the F-layer height was also detected by the MU radar at Shigaraki. Thermospheric wind variations were observed by the MU radar through ion drift measurement and by a Fabry-Perot interferometer (FPI) through a Doppler shift of the 630-nm airglow line at Shigaraki. The wind data show a turn of the meridional wind from -94 m/s (equatorward) to + 44 m/s (poleward) during the LSTID, indicating that an intense poleward wind in the thermosphere passed over Shigaraki as an atmospheric gravity wave and caused the observed ionospheric features of the LSTID. Intense poleward wind was also detected at mesospheric altitudes (95 - 100 km) by the MU radar ( through meteor echoes) and by the FPI ( through the 558-nm airglow) with a delay of similar to2 hours from the thermospheric wind, indicating downward phase progression of the wave. Generation of the observed poleward wind in the auroral zone was investigated using magnetic field data and auroral energy input estimated by the assimilative mapping of ionospheric electrodynamics (AMIE) technique. We suggest that simple atmospheric heating and/or the Lorentz force in the auroral zone do not explain the observed poleward wind enhancement.

DOI： 10.1029/2003JA010001

Statistical study of short-period gravity waves on OH and OI nightglow images at two separated sites Reviewed Open Access

Ejiri M., Shiokawa K., Ogawa T., Igarashi K., Nakamura T., Tsuda T.

Journal of Geophysical Research D Atmospheres Vol. 108 ( 21 ) 2003.11

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research D Atmospheres

Using airglow images of the near-infrared OH band (720-910 nm) and OI (557.7 nm) line, we investigated seasonal, latitudinal, and localt ime variations of short-period gravity waves. The images were obtained at two locations in Japan that are ∼1200 km apart, Rikubetsu (43.5°N, 143.8°E) and Shigaraki (34.9°N, 136.1°E), between October 1998 and October 1999. Our analysis has focused on small-scale gravity waves with wavelengths less than 40 km and dominant phase speeds of ∼20-50 m/s. Wave occurrences for both OH and OI at Rikubetsu and Shigaraki are significantly higher than 60%, with a slightly larger value in summer. The occurrences increase from evening to midnight. There are no obvious local time dependencies in horizontal wavelength, propagation direction, and phase speed. The propagation directions in summer are either northward or northeastward at both locations. However, in winter the propagation directions at Rikubetsu are generally westward (NW, W, and SW), whereas those at Shigaraki are only southwestward. From simultaneous wind observation by the MF radars at Wakkanai (45.4°N, 141.7°E) and Yamagawa (31.2°N, 130.6°E), we discuss possible influences of Doppler and thermal ducting, wind filtering, and source distribution of gravity waves propagating from the lower atmosphere to the airglow heights in the mesopause region. Copyright 2003 by the American Geophysical Union.

DOI： 10.1029/2002JD002795

Statistical study of short-period gravity waves in OH and OI nightglow images at two separated sites Reviewed

MK Ejiri, K Shiokawa, T Ogawa, K Igarashi, T Nakamura, T Tsuda

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 108 ( D21 ) 2003.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

[1] Using airglow images of the near-infrared OH band (720 - 910 nm) and OI (557.7 nm) line, we investigated seasonal, latitudinal, and local time variations of short-period gravity waves. The images were obtained at two locations in Japan that are similar to 1200 km apart, Rikubetsu (43.5 degreesN, 143.8 degreesE) and Shigaraki (34.9 degreesN, 136.1 degreesE), between October 1998 and October 1999. Our analysis has focused on small-scale gravity waves with wavelengths less than 40 km and dominant phase speeds of similar to 20 - 50 m/s. Wave occurrences for both OH and OI at Rikubetsu and Shigaraki are significantly higher than 60%, with a slightly larger value in summer. The occurrences increase from evening to midnight. There are no obvious local time dependencies in horizontal wavelength, propagation direction, and phase speed. The propagation directions in summer are either northward or northeastward at both locations. However, in winter the propagation directions at Rikubetsu are generally westward ( NW, W, and SW), whereas those at Shigaraki are only southwestward. From simultaneous wind observation by the MF radars at Wakkanai (45.4 degreesN, 141.7 degreesE) and Yamagawa (31.2 degreesN, 130.6 degreesE), we discuss possible influences of Doppler and thermal ducting, wind filtering, and source distribution of gravity waves propagating from the lower atmosphere to the airglow heights in the mesopause region.

DOI： 10.1029/2002JD002795

Bi-directional electrons in the near-Earth plasma sheet Reviewed Open Access

Shiokawa K, Baumjohann W, Paschmann G

ANNALES GEOPHYSICAE Vol. 21 ( 7 ) page： 1497 - 1507 2003.7

Optical and radio measurements of a 630-nm airglow enhancement over Japan on 9 September 1999 Reviewed Open Access

Otsuka, Y, Kadota, T, Shiokawa, K, Ogawa, T, Kawamura, S, Fukao, S, Zhang, SR

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 108 ( A6 ) 2003.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

Using a comprehensive data set from optical and radio instruments, we investigate a midnight brightness wave that appeared in 630-nm airglow images over Japan on the night of 9 September 1999. This may be the first such observation of the brightness wave with an all-sky imager in the East-Asian longitudinal sector. The imager at Shigaraki (35.6°N, 136.1°E) tracked a north-northeastward propagation of the wave with an apparent velocity of 500 m s-1 after midnight. Ionosonde observations at five stations in Japan showed that rapid descent of the F2 layer propagated northward beyond 35°N with decreasing amplitude. Incoherent scatter observations with the MU radar at Shigaraki also revealed that the F2 peak altitude decreased from 360 to 280 km during the event. During the F2 layer descent the altitude profile of the electron density became sharp, enhancing the F 2 peak electron density. After the F2 layer altitude reached 280 km, electron density in the F2 layer rapidly decreased because of increased neutral density at low altitude. A Fabry-Perot interferometer (FPI) at Shigaraki observed northward neutral winds of 10-70 m s-1 during the event. A model calculation demonstrates that the meridional winds estimated from the MU radar electron density profiles are fairly consistent with those observed with the FPI. From these results we conclude that the observed northward wind enhancements, probably caused by the midnight temperature maximum, pushed down the plasma in the F2 layer to lower altitudes along the geomagnetic field to cause the 630-nm airglow intensity enhancement. Copyright 2003 by the American Geophysical Union.

DOI： 10.1029/2002JA009594

夜間に観測される海外VHF帯局電波と plasma bubble の相関について Reviewed

P345 オーストラリア・ダーウィンで観測された大気光画像中の重力波の統計解析 Reviewed Open Access

鈴木臣, 塩川和夫, 大塚雄一, 小川忠彦

大会講演予講集 Vol. 83 page： 416 2003.5

長嶋郁生, 中田裕之, 大塚雄一, 鷹野敏明, 坂井来人, 塩川和夫, 小川忠彦

大気電気研究 Vol. 62 page： 91 - 92 2003.4

Ground and satellite observations of nighttime medium-scale traveling ionospheric disturbance at midlatitude Reviewed Open Access

K Shiokawa, Y Otsuka, C Ihara, T Ogawa, FJ Rich

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 108 ( A4 ) 2003.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

[1] We have investigated a nighttime medium-scale traveling ionospheric disturbance (MSTID) observed by an airglow imager at Shigaraki (34.9degreesN, 25.4degreesMLAT), Japan, on 17 May 2001. The structure was identified in the airglow images of OI (630.0 nm and 777.4 nm) as NW-SE band structures (horizontal wavelength: 230 km) moving southwestward with a velocity of 50 m/s. Neutral wind velocity was measured simultaneously from the Doppler shift of the 630.0-nm emission by a Fabry-Perot interferometer at Shigaraki. From these parameters, we performed model calculations of MSTIDs generated by gravity waves and by an oscillating electric field. We found that for the case of gravity waves, the estimated vertical wavelength was too small to explain the observed amplitudes of airglow intensity. For the case of the electric field, we found that an electric field oscillation of similar to1.2 mV/m was sufficient to reproduce the observed airglow amplitudes. This modeled electric field was comparable to that observed by the DMSP F15 satellite as it passed over Shigaraki during our observing period on 17 May 2001. The DMSP ion drift data show that the oscillation of the polarization electric field correlated with the MSTID structure in the airglow image, suggesting that the polarization electric field plays an important role in the generation of MSTIDs.

DOI： 10.1029/2002JA009639

内部磁気圏ミッションの提案

塩川和夫, 関加奈子, 三好由純, 小原隆博, 小野高幸

第3回宇宙科学シンポジウム proceeding page： 435 - 443 2003.4

Statistical study of nighttime medium-scale traveling ionospheric disturbances using midlatitude airglow images Reviewed Open Access

Shiokawa, K, Ihara, C, Otsuka, Y, Ogawa, T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 108 ( A1 ) 2003.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Blackwell Publishing Ltd

We have investigated statistical characteristics of the nighttime medium-scale Traveling ionospheric disturbances (MSTIDs) observed in 630-nm airglow images at two stations, Rikubetsu (43.5°N, 34.8°MLAT) and Shigaraki (34.9°N, 25.4°MLAT), in Japan for 1998-2000 near the solar maximum period. Most of the observed MSTIDs propagate southwestward in the images. The typical wavelength, velocity, period, and amplitude are 100-300 km, 50-100 m/s, 0.5-1.5 h, and 5-15%, respectively. Seasonal variations in these parameters are not clear. The occurrence rate has a major peak (50-60%) in summer that appears ∼2 months earlier at lower latitudes and a minor peak in winter. Similar occurrence.characteristics are obtained from midlatitude spread-F signatures using multipoint ionosonde data in Japan, though the coincidence of the spread-F and the MSTIDs in airglow images is only 10-15%. Copyright 2003 by the American Geophysical Union.

DOI： 10.1029/2002JA009491

A localized structure in OH airglow images near the mesopause region Reviewed Open Access

Shiokawa K, Ejiri MK, Ogawa T, Yamada Y, Fukunishi H, Igarashi K, Nakamura T

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 108 ( D2 ) 2003.1

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research: Atmospheres

An intense localized airglow-depletion structure was observed in OH airglow images (emission altitude ∼86 km) at Shigaraki (34.9°, 136.1°) on 19 December 1998. The structure was a single-band airglow depletion with a small horizontal width (∼15 km) but a large amplitude (∼34% from the average intensity). Airglow rotational temperature indicated a large temperature lapse rate at this time as a result of strong semidiurnal variation. We suggest that nonlinear wave-wave interaction is the most likely cause of this localized structure.

DOI： 10.1029/2002JD002462

A two-channel Fabry-Perot interferometer with thermoelectric-cooled CCD detectors for neutral wind measurement in the upper atmosphere Reviewed Open Access

Shiokawa K, Kadota T, Otsuka Y, Ogawa T, Nakamura T, Fukao S

EARTH PLANETS AND SPACE Vol. 55 ( 5 ) page： 271-275 2003

Seasonal variations of medium-scale gravity wave parameters in the lower thermosphere obtained from spectral airglow temperature imager observations at Shigaraki, Japan Reviewed Open Access

NM Gavrilov, K Shiokawa, T Ogawa

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 107 ( D24 ) page： 7 - 10 2002.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

[1] A method of statistical analysis is used to study parameters of the medium-scale internal gravity waves (IGWs) from the data of the spectral airglow temperature imager (SATI) observations of the OH and O-2 nightglow emissions at Shigaraki, Japan (35degreesN, 136degreesE) during April 1998 to May 2001. Average relative magnitudes of spectral components of airglow variations are 1.8-2.4% for the emission rates and 0.5-1% for the rotational temperature in different seasons. Distributions of periods, horizontal wavelengths, and phase speeds have the main maxima at 0.5-2 hours, 100-500 km, and 50-150 m/s, respectively. In winter, the distributions of propagation azimuths are broad with a dominance in the northwest sector and in the southern half of the sky for OH and in the northwest and southeast sectors for O-2. In spring and summer, IGWs propagate mainly to the northern half of the sky with larger occurrence in the northeast sector for OH emission. Seasonal variations of the average and median IGW magnitudes do not exceed 20-30% and are not stable. In winter, IGWs have maximum occurrence with larger magnitudes, horizontal wavelengths, and phase speeds, particularly at azimuths of 90-210 deg. These results are compared with previous studies.

DOI： 10.1029/2001JD001469

Magnetospheric responses to sudden and quasiperiodic solar wind variations Reviewed Open Access

KH Kim, CA Cattell, DH Lee, K Takahashi, K Yumoto, K Shiokawa, FS Mozer, M Andre

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 107 ( A11 ) 2002.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

[1] On April 13 (day 103), 2001, 0700-1400 UT, the Polar satellite experienced different plasma regimes (i.e., magnetosphere, magnetosheath, and solar wind) because of the solar wind dynamic pressure variations and its high orbital inclination near the subsolar magnetopause meridian. When Polar was in the magnetosheath, quasiperiodic spacecraft potential (SP) variations, corresponding to density variations, with a recurrence time of similar to3-10 min were observed. Using simultaneous solar wind observations, it was confirmed that the magnetosheath SP variations were inherent in the solar wind. We observed an almost one-to-one correspondence between the SP variations and the geomagnetic field perturbations at lower latitudes (L = 1.1-2.8) on the nightside. At higher latitudes (L = 2.9-6.1) on the dayside, however, the field perturbations are more complicated than the magnetosheath SP variations. This suggests that if the magnetospheric perturbations produced by the external source (solar wind/magnetosheath pressure variations) deeply penetrate into the magnetosphere, the lower-latitude data on the nightside are important to monitor the external source variations. In addition, we observed the radial electric field oscillations excited nearly simultaneously with the magnetic field enhancement, associated with a sudden increase in the solar wind dynamic pressure, when Polar was in the magnetosphere. These oscillations may be considered as transient standing Alfven waves excited by externally applied pressure changes as reported by previous studies.

DOI： 10.1029/2002JA009342

New auroral spectrometer using an acousto-optic tunable filter Reviewed

Shiokawa Kazuo, Katoh Yasuo, Satoh Mitsugi, Ogawa Tadahiko, Taguchi Makoto, Yamagishi Hisao

Advances in polar upper atmosphere research Vol. 16 page： 146 - 156 2002.9

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：National Institute of Polar Research

This paper reports the performance and capability of a newly developed zenith spectrometer (for measurements of airglow and aurora) that uses an acousto-optic tunable filter (AOTF). The AOTF can scan the pass-band of the spectrometer between 450 and 700 nm with a bandwidth of 2-3 nm by changing the RF driver frequency from 180 to 100 MHz. The absolute sensitivity of the spectrometer is 〜0.1-1.5 counts/Rayleigh/s per spectral step. The spectrometer is fully automated. The O I (557.7 nm) airglow line can be clearly identified in test observations of midlatitude airglow performed at Shigaraki Observatory, Japan. Based on an estimate of the signal-to-noise ratio, we conclude that the full auroral spectrum (450-700) nm can be measured by the AOTF spectrometer with a time resolution of 〜100 s and a signal-to-noise ratio of 〜100 for an auroral emission intensity of 10 kR. An example of the auroral spectra is shown for observations made at Syowa Station in Antarctica.

Geomagnetic conjugate observations of equatorial airglow depletions Reviewed

Y Otsuka, K Shiokawa, T Ogawa, P Wilkinson

GEOPHYSICAL RESEARCH LETTERS Vol. 29 ( 15 ) 2002.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We report for the first time large-scale equatorial F-region airglow depletions extending to low-midlatitudes in both hemispheres. The observational sites were located at low-midlatitude geomagnetic conjugate points. Clear depletions of 630.0-nm airglow intensity due to equatorial plasma bubbles were simultaneously observed with two all-sky imagers at Sata, Japan (magnetic latitude 24degreesN), and its geomagnetic conjugate point, Darwin, Australia (magnetic latitude 22degreesS), on the night of November 12, 2001. Airglow depletion regions with east-west scale sizes of 40-100 km extend poleward. The maximum apex altitude of the plasma bubbles is about 1,700 km over the geomagnetic equator. The depletions move eastward at about 100 m/s, without changing their structures. The Darwin depletion structures mapped onto the northern hemisphere along the geomagnetic field coincide closely with structures in the Sata images, even for the 40-km structure. These observations indicate that plasma depletions in the equatorial ionosphere elongate along the geomagnetic field lines.

DOI： 10.1029/2002GL015347

Multiple auroral brightenings and associated Pi 2 pulsations Reviewed Open Access

K Shiokawa, K Yumoto, JV Olson

GEOPHYSICAL RESEARCH LETTERS Vol. 29 ( 11 ) page： 32 - 1 2002.6

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

[1] All-sky auroral data at Kotzebue (KOT, 64.4degrees MLAT), Alaska, and magnetic field data from both high- and low-latitude stations are used to demonstrate the relation between multiple auroral brightenings and Pi 2 magnetic pulsations during an isolated substorm. At least five Pi 2 wave packets are identified in the magnetic field data around the end of the growth phase. Auroral luminosity variations do not show oscillations in the Pi 2 frequency range, though each Pi 2 wave packet has good correspondence with each small-scale auroral brightening and poleward motion. This fact may contradict the idea of high- latitude Pi 2 generation by oscillations of substorm field-aligned currents. We discuss possible reasons of this discrepancy from localization of the Pi 2 current system and low-energy electrons as the current carrier.

DOI： 10.1029/2001GL014583

A large-scale traveling ionospheric disturbance during the magnetic storm of 15 September 1999 Reviewed Open Access

K Shiokawa, Y Otsuka, T Ogawa, N Balan, K Igarashi, AJ Ridley, DJ Knipp, A Saito, K Yumoto

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 107 ( A6 ) 2002.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

[1] Using a comprehensive data set and model calculations, we have investigated a prominent large-scale traveling ionospheric disturbance (LSTID) observed in Japan (similar to37degrees-16degrees MLAT) on 15 September 1999, during a recovery phase of sequential storms. The LSTID was detected at 2300-2400 LT (1400-1500 UT) as an enhancement of the 630-nm airglow intensity (50 --> 350 R), a decrease in the F layer virtual height (at 2 MHz, 360 --> 200 km), an enhancement of f(o)F(2) (6 --> 8 MHz), and an enhancement of GPS total electron content (similar to1.0 x 10(16) m(-2)). Multipoint and imaging observations of these parameters show that the LSTID moved equatorward over Japan with a velocity of similar to400-450 m/s. From a comparison with the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) we conclude that an enhancement (250-300 m/s) of poleward neutral wind (that is propagating equatorward) caused these observational features of the LSTID at midlatitudes. To investigate generation of the LSTID by auroral energy input, we have used auroral images obtained by the Polar UVI instrument, magnetic field variations obtained at multipoint ground stations, and the empirical Joule heating rate calculated by the assimilative mapping of ionospheric electrodynamics (AMIE) technique. Intense auroral energy input was observed at 0800-1100 UT (4-6 hours before the LSTID), probably causing equatorward neutral wind at lower latitudes. It is likely that the poleward wind pulse that caused the observed LSTID was generated associated with the cessation of this equatorward wind. The effect of Lorentz force is also discussed.

DOI： 10.1029/2001JA000245

A large-scale traveling ionospheric disturbance during the magnetic storm of 15 September 1999 Reviewed Open Access

Shiokawa K., Otsuka Y., Ogawa T., Balan N., Igarashi K., Ridley A.J., Knipp D.J., Saito A., Yumoto K.

Journal of Geophysical Research Space Physics Vol. 107 ( A6 ) 2002.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

[1] Using a comprehensive data set and model calculations, we have investigated a prominent large-scale traveling ionospheric disturbance (LSTID) observed in Japan (∼37°-16° MLAT) on 15 September 1999, during a recovery phase of sequential storms. The LSTID was detected at 2300-2400 LT (1400-1500 UT) as an enhancement of the 630-nm airglow intensity (50→350 R), a decrease in the F layer virtual height (at 2 MHz, 360→200 km), an enhancement of F<inf>o</inf>F<inf>2</inf> (6→8 MHz), and an enhancement of GPS total electron content (∼1.0 x 1016 m-2). Multipoint and imaging observations of these parameters show that the LSTID moved equatorward over Japan with a velocity of ∼400-450 m/s. From a comparison with the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) we conclude that an enhancement (250-300 m/s) of poleward neutral wind (that is propagating equatorward) caused these observational features of the LSTID at midlatitudes. To investigate generation of the LSTID by auroral energy input, we have used auroral images obtained by the Polar UVI instrument, magnetic field variations obtained at multipoint ground stations, and the empirical Joule heating rate calculated by the assimilative mapping of ionospheric electrodynamics (AMIE) technique. Intense auroral energy input was observed at 0800-1100 UT (4-6 hours before the LSTID), probably causing equatorward neutral wind at lower latitudes. It is likely that the poleward wind pulse that caused the observed LSTID was generated associated with the cessation of this equatorward wind. The effect of Lorentz force is also discussed. Copyright 2002 by the American Geophysical Union.

DOI： 10.1029/2001JA000245

Dual-site imaging observations of small-scale wave structures through OH and OI nightglow emissions Reviewed

Ejiri MK, Shiokawa K, Ogawa T, Kubota M, Nakamura T, Tsuda T

GEOPHYSICAL RESEARCH LETTERS Vol. 29 ( 10 ) page： 85 - 1 2002.5

New auroral spectrometer using an aousto-optic tunable filter Reviewed

Shiokawa, K, Y. Katoh, M. Satoh, T. Ogawa, M. Taguchi, H. Yamagishi

Adv. Polar Upper Atmos. Res. Vol. 16 page： 146 - 156 2002.1

Observations and modeling of 630 nm airglow and total electron content associated with traveling ionospheric disturbances over Shigaraki, Japan Reviewed Open Access

Ogawa T, Balan N, Otsuka Y, Shiokawa K, Ihara C, Shimomai T, Saito A

EARTH PLANETS AND SPACE Vol. 54 ( 1 ) page： 45-56 2002

Imaging observations of the equatorward limit of midlatitude traveling ionospheric disturbances Reviewed Open Access

Shiokawa K, Otsuka Y, Ejiri MK, Sahai Y, Kadota T, Ihara C, Ogawa T, Igarashi K, Miyazaki S, Saito A

EARTH PLANETS AND SPACE Vol. 54 ( 1 ) page： 57 - 62 2002

Plasmaspheric electron content in the GPS ray paths over Japan under magnetically quiet conditions at high solar activity Reviewed Open Access

Balan N, Otsuka Y, Tsugawa T, Miyazaki S, Ogawa T, Shiokawa K

EARTH PLANETS AND SPACE Vol. 54 ( 1 ) page： 71 - 79 2002

The wave2000 campaign: overview and preliminary results Reviewed

Iwagami N, Shibaki T, Suzuki T, Yamada Y, Onishi H, Takahashi Y, Yamamoto H, Sekiguchi H, Mori K, Sano Y, Kubota M, Murayama Y, Ishii M, Oyama KI, Yoshimura R, Shimoyama M, Koizumi Y, Shiokawa K, Takegawa N, Nakamura T

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 64 ( 8-11 ) page： 1095 - 1104 2002

A stable auroral red arc observed over Japan after an interval of very weak solar wind Reviewed Open Access

Shiokawa K, Ogawa T, Oya H, Rich FJ, Yumoto K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 106 ( A11 ) page： 26091 - 26101 2001.11

Imaging observations of midlatitude ionospheric disturbances during the geomagnetic storm of February 12, 2000 Reviewed Open Access

Sahai Y, Shiokawa K, Otsuka Y, Ihara C, Ogawa T, Igarashi K, Miyazaki S, Saito A

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 106 ( A11 ) page： 24481 - 24492 2001.11

Small-scale gravity waves near the mesopause observed by four all-sky airglow imagers Reviewed Open Access

Ejiri MK, Shiokawa K, Ogawa T, Nakamura T, Maekawa R, Tsuda T, Kubota M

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Vol. 106 ( D19 ) page： 22793 - 22799 2001.10

Bi-directional electron distributions associated with near-tail flux transport Reviewed

Sergeev VA, Baumjohann W, Shiokawa K

GEOPHYSICAL RESEARCH LETTERS Vol. 28 ( 19 ) page： 3813 - 3816 2001.10

Three-channel imaging Fabry-Perot interferometer for measurement of mid-latitude airglow Reviewed

Shiokawa K, Kadota T, Ejiri MK, Otsuka Y, Katoh Y, Satoh M, Ogawa T

APPLIED OPTICS Vol. 40 ( 24 ) page： 4286-4296 2001.8

Clinical analysis and prognostic study of ossified ligamentum flavum of the thoracic spine Reviewed

K Shiokawa, J Hanakita, H Suwa, M Saiki, M Oda, M Kajiwara

JOURNAL OF NEUROSURGERY Vol. 94 ( 2 ) page： 221 - 226 2001.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER ASSOC NEUROLOGICAL SURGEONS

Object. A variety of factors may affect surgery-related outcome in patients with ossification of the ligamentum flavum (OLF) of the thoracic spine. The aim of this study was to determine these factors on the basis of preoperative clinical and radiological findings.
Methods. The authors treated 31 cases of symptomatic thoracic OLF between 1988 and 1999. The following factors were retrospectively studied: patient age, sex, morbidity level, initial symptoms, chief complaint, duration of symptoms, patellar reflex, Achilles reflex, computerized tomography (CT) finding, presence of intramedullary change determined by magnetic resonance imaging, coexistent spinal lesions, preoperative grade, and postoperative grade.
A decompressive laminectomy was performed in all cases. In 29 patients (94%) improved symptoms were demonstrated postoperatively. In terms of functional prognosis, the preoperative duration of symptoms was significantly shorter in the group of patients with excellent outcomes than in those with fair outcomes (p < 0.05).
No significant difference was observed in the correlation between other factors. To evaluate the degree of preoperative thoracic stenosis and the severity/extent of OLF-induced spinal compression, we used an original OLF CT scoring system. A score of excellent on the CT scale tended to indicate an excellent prognosis (p < 0.01).
Conclusions. Thoracic OLF frequently develops in the lower-thoracic spine in middle-aged men, and it is complicated by various spinal lesions in many cases. Early diagnosis and treatment are important for understanding the clinical symptoms and imaging diagnosis because the present findings suggest that a delay in diagnosis and treatment correlates with the functional prognosis postoperatively.

DOI： 10.3171/spi.2001.94.2.0221

Traveling ionospheric disturbances detected in the FRONT campaign Reviewed Open Access

Saito A, Nishimura M, Yamamoto M, Fukao S, Kubota M, Shiokawa K, Otsuka Y, Tsugawa T, Ogawa T, Ishii M, Sakanoi T, Miyazaki S

GEOPHYSICAL RESEARCH LETTERS Vol. 28 ( 4 ) page： 689 - 692 2001.2

A stable auroral red (SAR) arc observed over Japan after an interval of very weak solar wind Reviewed

J. Geophys. Res. Vol. 106 page： 26,091-26,101 2001

Cleavage pattern modulation of frog's egg under magnetic fields of 10 tesla order Reviewed

M Iwasaka, S Ueno, K Shiokawa

INTERNATIONAL JOURNAL OF APPLIED ELECTROMAGNETICS AND MECHANICS Vol. 14 ( 1-4 ) page： 327 - 330 2001

Language：English Publishing type：Research paper (scientific journal) Publisher：IOS PRESS

In the present study, a possible influence of intense magnetic fields on cleavage patterns during the early embryonic development of frogs was studied. The early cleavages in Xenopus laevis were disordered by horizontal magnetic fields of 10 T order. However, the magnetic field effect did not remain until when they become tadpoles.

Three-channel imaging Fabry-Perot interferometer for midlatitude airglow measurement Reviewed

Shiokawa, K, T. Kadota, M. K. Ejiri, Y. Otsuka, Y. Katoh, M. Satoh, T. Ogawa

Appl. Opt. Vol. 40 ( 24 ) page： 4286 - 4296 2001

Thoracic spinal cord herniation presenting with Brown-Séquard syndrome Reviewed Open Access

M. Kajiwara, J. Hanakita, H. Suwa, K. Shiokawa, M. Saiki, M. Oda

Japanese Journal of Neurosurgery Vol. 10 ( 6 ) page： 389 - 393 2001

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Congress of Neurological Surgeons

An increasing number of cases involving spinal cord herniation have been reported since the advent of magnetic resonance imaging (MRI). A 57-year-old woman with a history of previous blunt thoracic back trauma resulting from a traffic accident 9 years ago, presented with Brown-Séquard syndrome. MRI of the thoracic spine revealed ventral displacement of the spinal cord at Th4/5 and a dorsal intradural arachnoid cyst. At surgery, a dural defect about 15 mm in length was identified, into which gliotic spinal cord with arachnoid membrane herniated. The herniated spinal cord was reduced and the dural defect was repaired using Goretex. A postoperative MRI showed the spinal cord in the normal position, and her clinical symptoms improved. We reviewed the characteristics of spinal cord herniations according to the reported cases. These cases can be divided into 2 categories : spontaneous or idiopathic one and post-traumatic ones. The present case is thought to be an idiopathic one, in spite of the patient's blunt back trauma.

DOI： 10.7887/jcns.10.389

Seasonal variation of gravity waves with various temporal and horizontal scales in the MLT region observed with radar and airglow imaging Reviewed

T Nakamura, T Tsuda, R Maekawa, M Tsutsumi, K Shiokawa, T Ogawa

MIDDLE ATMOSPHERE TEMPORAL AND SPATIAL STRUCTURES Vol. 27 ( 10 ) page： 1737 - 1742 2001

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Seasonal variations of activity and horizontal propagation direction of gravity waves in the MLT region at mid-latitude over Shigaraki, Japan (35 N) are investigated for various time and spatial scales using the MU radar observations and recent airglow imaging observations. Semiannual variation with solsticial maxima and equinoctial minima are generally observed for short period (<5 hours) gravity waves. Eastward preference in summer and westward in winter for horizontal propagation direction is generally observed except for small scale (horizontal wavelength < about 15 km) gravity waves. Meridional preference such as northward in summer and southward in winter is also found in airglow imaging and some of the radar results. The preferential propagation direction between northward and eastward in summer is more commonly observed at various horizontal and time scales. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0273-1177(01)00310-6

"Fine structure" of the storm-substorm relationship: Ion injections during Dst decrease Reviewed

Coil embolization of a lacerated lumbar artery due to compression fracture Reviewed Open Access

M. Kajiwara, J. Hanakita, H. Suwa, K. Shiokawa, M. Saiki, M. Oda, N. Nakajima

Japanese Journal of Neurosurgery Vol. 10 ( 7 ) page： 465 - 468 2001

Radiological examinations and surgical approaches for far-lateral lumbar disc herniation Reviewed Open Access

J. Hanakita, H. Suwa, K. Shiokawa, M. Saiki, M. Oda, M. Kajiwara, T. Sato

Japanese Journal of Neurosurgery Vol. 10 ( 10 ) page： 647 - 653 2001

Multi-point observation of short-period mesospheric gravity waves over Japan during the FRONT campaign Reviewed Open Access

Shiokawa K, Ejiri MK, Otsuka Y, Ogawa T, Kubota M, Igarashi K, Saito A, Nakamura T

GEOPHYSICAL RESEARCH LETTERS Vol. 27 ( 24 ) page： 4057 - 4060 2000.12

Traveling ionospheric disturbances observed in the OI 630-nm nightglow images over Japan by using a multipoint imager network during the FRONT campaign Reviewed Open Access

Kubota M, Shiokawa K, Ejiri MK, Otsuka Y, Ogawa T, Sakanoi T, Fukunishi H, Yamamoto M, Fukao S, Saito A

GEOPHYSICAL RESEARCH LETTERS Vol. 27 ( 24 ) page： 4037 - 4040 2000.12

Comprehensive imaging observations of midlatitude ionospheric disturbances during storm time substorms Reviewed Open Access

Shiokawa K, Otsuka Y, Ogawa T, Igarashi K, Miyazaki S, Rich FJ, Saito A, Yumoto Y

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 105 ( A12 ) page： 27067 - 27080 2000.12

Distant lunar sodium tail observed in the Japanese local-time sector during the Leonid meteor shower of 1998 Reviewed

Shiokawa K, Ejiri MK, Ogawa T, Nakamura T

JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS Vol. 105 ( E10 ) page： 24621 - 24626 2000.10

A search for the springtime transition of lower thermospheric atomic oxygen using long-term midlatitude airglow data Reviewed

Shiokawa K, Kiyama Y

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 62 ( 13 ) page： 1215-1219 2000.9

Geomagnetic negative impulse due to a magnetic cloud observed on May 13, 1995 Reviewed Open Access

Takeuchi, T. T. Araki, H. Luehr, O. Rasmussen, J. Watermann, D. K. Milling, I. R. Mann, K. Yumoto, K. Shiokawa, T. Nagai

J. Geophys. Res. Vol. 105 ( A8 ) page： 18835 - 18846 2000.8

High- and low-altitude observations of adiabatic parameters associated with auroral electron acceleration Reviewed

Shiokawa K, Baumjohann W, Haerendel G, Fukunishi H

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 105 ( A2 ) page： 2541 - 2550 2000.2

A search for the springtime transition oflower thermospheric atomic oxygen using long-term midlatitude airglow data Reviewed

J. Atmos. Solar Terr. Phys. Vol. 62 page： 1215-1219 2000

Multi-point observations of short-period mesospheric gravity waves over Japan during the FRONT campaign

Geophys. Res. Lett. Vol. 24 page： 4057-4060 2000

Integrating-sphere calibration of all-sky cameras for nightglow measurements Reviewed

Shiokawa K, Katoh Y, Satoh M, Ejiri MK, Ogawa T

ADVANCES IN REMOTE SENSING OF THE ATMOSPHERE FROM SPACE AND FROM THE GROUND Vol. 26 ( 6 ) page： 1025-1028 2000

IA Daglis, Y Kamide, C Mouikis, GD Reeves, ET Sarris, K Shiokawa, B Wilken

INNER MAGNETOSPHERE DYNAMICS Vol. 25 ( 12 ) page： 2369 - 2372 2000

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON PRESS LTD

Following a long period of consensus on the storm-substorm relationship, a dispute on this topic has emerged in recent years. The importance of substorms for the buildup of the terrestrial ring current, which is the major element of magnetic storms, has been questioned in several studies. This paper is an effort to assess the "fine structure" of the storm-substorm relationship, by investigating the correlation between the changes in Dst and the substorm-associated O+ enhancements in the inner magnetosphere during the storm main phase. For this purpose we use energetic ion measurements from the Magnetospheric Ion Composition Spectrometer (MICS) on board the Combined Release and Radiation Effects Satellite (CRRES), and the newly produced high-resolution (5-min) Dst index for the intense storm of June 5, 1991. Substorm signatures from both MICS measurements and ground magnetometers correlate well with changes in the Dst decrease rate. This implies a significant influence of substorm occurrence on storm dynamics. (C) 2000 COSPAR. Published by Elsevier Science Ltd.

DOI： 10.1016/S0273-1177(99)00525-6

Three cases of hematoma formation after nerve block therapy or lumbar anesthesia Reviewed Open Access

M. Oda, J. Hanakita, H. Suwa, K. Shiokawa, M. Saiki, T. Sato, M. Kajiwara

Japanese Journal of Neurosurgery Vol. 9 ( 12 ) page： 807 - 811 2000

Flow braking and the substorm current wedge Reviewed Open Access

Birn J, Hesse M, Haerendel G, Baumjohann W, Shiokawa K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 104 ( A9 ) page： 19895 - 19903 1999.9

Calibration of all-sky cameras and tilting-photometers using an integrating-sphere and a spectrometer (in Japanese) Reviewed Open Access

Katoh Yasuo, Shiokawa Kazuo, Satoh Mitsugi, Ejiri Mitsumu K., Ogawa Tadahiko

Antarctic record Vol. 43 ( 1 ) page： 1-15 1999.3

Language：English Publishing type：Research paper (scientific journal)

We report calibration of the optical instruments of the Optical Mesosphere Thermosphere Imagers (OMTI) using facilities at the National Institute of Polar Research. OMTI has been developed to investigate dynamics of the upper atmosphere through nocturnal airglow emissions. OMTI consist of an imaging Fabry-Perot interferometer, three all-sky cooled-CCD cameras, three tilting-photometers, and a spectral airglow temperature imager (SATI). The all-sky cameras and the photometers have been calibrated using a 2-m integrating-sphere and a spectrometer. Absolute sensitivity and image-flattening data are obtained together with filter transmission functions. Inhomogeneity of transmission function on the filter surface is found from the calibration using the spectrometer. We also find that filters with highly-flattened image-quality surfaces may cause serious Newton's Ring pattern on final images. Examples of the data are shown for the cameras and the photometers based on the airglow observation at Shigaraki (35°N, 136°E), Japan.

DOI： 10.15094/00009066

Calibration of all-sky cameras and tilting-photometers using an integrating-sphere and a spectrometer Reviewed Open Access

Katoh Y., Shiokawa K., Satoh M., Ejiri M.K., Ogawa T.

Antarctic Record Vol. 43 ( 1 ) page： 1 - 15 1999.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Antarctic Record

DOI： 10.15094/00009066

Development of optical mesosphere thermosphere imagers (OMTI) Reviewed Open Access

Shiokawa K, Katoh Y, Satoh M, Ejiri MK, Ogawa T, Nakamura T, Tsuda T, Wiens RH

EARTH PLANETS AND SPACE Vol. 51 ( 7-8 ) page： 887-896 1999

Height measurements of nightglow structures observed by all-sky imagers Reviewed

Kubota M, Ishii M, Shiokawa K, Ejiri MK, Ogawa T

MESOPAUSE AND EXTRA-TERRESTRIAL INFLUENCES ON THE OZONE LAYER Vol. 24 ( 5 ) page： 593-596 1999

Simultaneous DMSP and CRRES observation of broadband electrons during a storm-time substorm on March 25, 1991 Reviewed

Shiokawa K, Anderson RR, Daglis IA, Hughes WJ, Wygant JR

PHYSICS AND CHEMISTRY OF THE EARTH PART C-SOLAR-TERRESTIAL AND PLANETARY SCIENCE Vol. 24 ( 1-3 ) page： 281 - 285 1999

Comment on "Braking of high-speed flows in the near-Earth tail" - Reply Reviewed

Haerendel G, Shiokawa K, Baumjohann W

GEOPHYSICAL RESEARCH LETTERS Vol. 25 ( 18 ) page： 3503 - 3503 1998.9

Reply Reviewed Open Access

Haerendel G., Shiokawa K., Baumjohann W.

Geophysical Research Letters Vol. 25 ( 18 ) 1998.9

Cloning and expression of an α-2,8-polysialyltransferase (STX) from Xenopus laevis Reviewed Open Access

Kudo, M; Takayama, E; Tashiro, K; Fukamachi, H; Nakata, T; Tadakuma, T; Kitajima, K; Inoue, Y; Shiokawa, K

GLYCOBIOLOGY Vol. 8 ( 8 ) page： 771 - 777 1998.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Glycobiology

Polysialic acid (polySia) is a carbohydrate structure found on neural cell adhesion molecules (N-CAM). Two polysialyltransferases (polySiaTs) that catalyze synthesis of polySia have been described, and designated PST-1/PST/ST8SiaIV and STX/ST8SiaII. We cloned a polySiaT (xSTX) from a nonmammalian vertebrate, Xenopus laevis. xSTX had 80% amino acid similarity to the rat STX. This clone induced polySia expression when transfected into polySia-negative COS-1 cells. Northern blot analysis of whole embryos at different stages of development revealed that xSTX mRNA was most abundantly expressed in premetamorphic stages. The relative level of xSTX and N-CAM mRNAs was also examined and found to change in parallel to the extent of polysialylation on N-CAM. In adult tissues, the expression of xSTX mRNA was restricted to brain, eye and heart, which also expressed polySia. These results suggest that xSTX is the major enzyme responsible for the synthesis of polysialylated N-CAM in embryos at certain stages of development and also in adult tissues.

DOI： 10.1093/glycob/8.8.771

PubMed

Azimuthal pressure gradient as driving force of substorm currents Reviewed

Shiokawa K, Haerendel G, Baumjohann W

GEOPHYSICAL RESEARCH LETTERS Vol. 25 ( 7 ) page： 959-962 1998.4

High-speed ion flow, substorm current wedge, and multiple Pi 2 pulsations Reviewed Open Access

Shiokawa K, Baumjohann W, Haerendel G, Paschmann G, Fennell JF, Friis-Christensen E, Luhr H, Reeves GD, Russell CT, Sutcliffe PR, Takahashi K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 103 ( A3 ) page： 4491 - 4507 1998.3

Two spacecraft observations of a reconnection pulse during an auroral breakup Reviewed Open Access

Petrukovich AA, Sergeev VA, Zelenyi LM, Mukai T, Yamamoto T, Kokubun S, Shiokawa K, Deehr CS, Budnick EY, Buchner J, Fedorov AO, Grigorieva VP, Hughes TJ, Pissarenko NF, Romanov SA, Sandahl I

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 103 ( A1 ) page： 47 - 59 1998.1

Two spacecraft observations of a reconnection pulse during an auroral breakup Reviewed Open Access

Petrukovich A.A., Sergeev V.A., Zelenyi L.M., Mukai T., Yamamoto T., Kokubun S., Shiokawa K., Deehr C.S., Budnick E.Y., Büchner J., Fedorov A.O., Grigorieva V.P., Hughes T.J., Pissarenko N.F., Romanov S.A., Sandahl I.

Journal of Geophysical Research Space Physics Vol. 103 ( A1 ) page： 47 - 59 1998

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

At 1130 UT on November 28, 1995, two spacecraft, Interball-Tail and Geotail, were in a favorable position to study the plasma sheet activity and an auroral breakup observed on the ground near the spacecraft ionospheric footpoints. Both spacecraft were near the neutral sheet, and they were nearly aligned along the magnetic meridian. During the auroral breakup observed at the equatorward half of the auroral oval (also registered as an AKR burst at Interball) both spacecraft simultaneously detected signatures of a reconnection pulse: The earthward plasma streaming and magnetic field dipolarization were observed at 12 R<inf>E</inf> at Interball, while the tailward energetic ion beam, then the tailward flow and the passage of a plasmoid were observed at 28 R<inf>E</inf> at Geotail. This pulse seem to proceed inside of the plasma sheet closed field lines, in the region of small (∼1 nT) background magnetic field at the neutral sheet. At Interball position the onset of fast earthward ion flow, likely initiated by the reconnection pulse, was followed by other manifestations (dipolarization, enhancements of the magnetic turbulence and the energetic particle flux, the intensification of field-aligned currents). Auroral observations showed initial brightening delayed an approximately l min after the commencement of the reconnection pulse. The auroral intensification was not accompanied by a significant magnetic disturbance on the ground, and therefore the event can be classified as the pseudobreakup. We estimate magnetic flux transport characteristics and possible location of the onset region in the plasma sheet. We conclude that observations during this event are consistent with the initiation of an auroral breakup by some disturbance (e.g., Alfven wave) generated by the reconnection pulse that commenced in the neutral sheet at ∼15 R<inf>E</inf> distance. Copyright 1998 by the American Geophysical Union.

DOI： 10.1029/97JA02296

High-speed ion flow, substorm current wedge, and multiple Pi 2 pulsations Reviewed Open Access

Shiokawa K., Baumjohann W., Haerendel G., Paschmann G., Fennell J.F., Friis-Christensen E., Lühr H., Reeves G.D., Russell C.T., Sutcliffe P.R., Takahashi K.

Journal of Geophysical Research Space Physics Vol. 103 ( A3 ) page： 4491 - 4507 1998

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Geophysical Research Space Physics

We have studied the onset timing of earthward high-speed ion flow observed by the AMPTE/IRM satellite at 12.3 Earth radii (R<inf>E</inf>) and 0100 MLT in the central plasma sheet during an isolated substorm event on March 1,1985. The timing of this onset is compared with that of the substorm current wedge and Pi 2 magnetic pulsations observed by a large number of ground-based stations and the AMPTE/CCE, GOES 5, and ISEE 1 satellites and with that of high-energy particle injection observed at Los Alamos geosynchronous satellite 1982-019. The onset of earthward high-speed flow is observed 3 min before the onset of the global current wedge formation and 6 min before the onset of high-energy particle injection. The three bursts of the high-speed flow observed at AMPTE/IRM are likely to correspond to three compressional pulses observed at AMPTE/CCE at 6 R<inf>E</inf> and three Pi 2 wave packets observed at midlatitude ground stations. On the basis of these observations we conclude that the substorm current wedge is caused by inertia current and the current due to flow shear at the braking point of the earthward high-speed flow during the initial stage of the substorm expansion phase. The braking point is well separated from the near-Earth neutral line. It is also suggested that the compressional pulses and fluctuations of field-aligned currents generated at the flow braking point can be the initial cause of the Pi 2 magnetic pulsations in the inner magnetosphere. Copyright 1998 by the American Geophysical Union.

DOI： 10.1029/97JA01680

Quasi-periodic poleward motions of morningside Sun-aligned arcs: A multievent study Reviewed Open Access

Shiokawa K, Ogino T, Hayashi K, McEwen DJ

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 102 ( A11 ) page： 24325-24332 1997.11

A multievent study of broadband electrons observed by the DMSP satellites and their relation to red aurora observed at midlatitude stations Reviewed Open Access

Shiokawa K, Meng CI, Reeves GD, Rich FJ, Yumoto K

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 102 ( A7 ) page： 14237 - 14253 1997.7

Anomalous sudden commencement on March 24, 1991 Reviewed Open Access

Araki, T, S. Fujitani, M. Emoto, K. Yumoto, K. Shiokawa, T. Ichinose, H. Luehr, D. Orr, D. Milling, H. Singer, G. Rostoker, S. Tsunomura, Y. Yamada, C.F. LiuTohru Araki

J. Geophys. Res. Vol. 102 ( A7 ) page： 14075 - 14086 1997.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

An anomalous geomagnetic sudden commencement (SC) occurred on March 24, 1991. It is characterized by an exceptionally large and sharp impulse observed in its initial part along the noon meridian in middle and low latitudes. The analysis of the SC was made by using high time resolution digital data from the 210 degrees Meridian Magnetometer Chain in the west Pacific, Sub-Auroral Magnetometer Network (SAMNET) in the United Kingdom and southern Scandinavia, the EISCAT Magnetometer Cross in northern Scandinavia and Svalbard, and Canopus in Canada together with other ground and satellite (GOES 6, GOES 7, CRRES, and GMS) data. The results of the analysis suggest that the pulse observed at lower-latitude ground stations was caused by the propagation of a strong magnetospheric compression of short duration (less than 1 min) which has never been observed before this event. The HF Doppler observation in Kyoto near local noon seems to be consistent with existence of the bipolar electric field associated with the propagating compressional magnetic pulse. The SAMNET stations and CRRES in the early morning also detected positive pulses which delays 30-50 s from the pulses in noon sector, Although the delay in the peak time of the pulse observed on the ground is consistent with ionospheric hydromagnetic wave propagation from the dayside to the nightside with finite speed, the initial onset time of the pulse on the ground was almost simultaneous everywhere suggesting the existence of an ''almost instantaneous'' propagation mode below the ionosphere.

DOI： 10.1029/96JA03637

Broadband electrons observed by the DMSP satellites during storm-time substorms (extended abstract) Reviewed

Braking of high-speed flows in the near-Earth tail Reviewed

Shiokawa K, Baumjohann W, Haerendel G

GEOPHYSICAL RESEARCH LETTERS Vol. 24 ( 10 ) page： 1179-1182 1997.5

Shiokawa Kazuo

Proceedings of the NIPR Symposium on Upper Atmosphere Physics Vol. 10 page： 151 - 153 1997.1

A study of the November 15, 1993 transpolar arc Reviewed Open Access

Zhang Y, McEwen DJ, Yumoto K, Shiokawa K, Hayashi K

JOURNAL OF GEOMAGNETISM AND GEOELECTRICITY Vol. 49 page： S141-S149 1997

Fields and flows at geotail during a moderate substorm Reviewed

McPherron RL, Nakamura R, Kokubun S, Kamide Y, Shiokawa K, Yumoto K, Mukai T, Saito Y, Hayashi K, Nagai T, Ables S, Baker DN, FriisChristensen E, Fraser B, Hughes T, Reeves G, Singer H

RESULTS OF THE IASTP PROGRAM Vol. 20 ( 4-5 ) page： 923 - 931 1997

Characterization of the major core structures of the α2→8-linked polysialic acid-containing glycan chains present in neural cell adhesion molecule in embryonic chick brains Reviewed Open Access

Kudo M., Kitajima K., Inoue S., Shiokawa K., Morris H.R., Dell A., Inoue Y.

Journal of Biological Chemistry Vol. 271 ( 51 ) page： 32667 - 32677 1996.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Biological Chemistry

To gain more insight into the possible functional significance of the core glycan chain(s) on which polysialylation takes place in polysialic acid (poly-Sia)-containing glycoproteins, the structure of the core glycans in the embryonic form of chick brain neural cell adhesion molecule (N-CAM) were examined using chemical and instrumental techniques. The following new structural features, which had not been reported by the early pioneering study by Finne (Finne, J. (1982) J. Biol. Chem. 257, 11966-11970), were revealed (Structure I). (i) Two distinct types of multiantennary N-linked glycans, i.e. tri- and tetra-antennary structures, are present; (ii) an α1→6-linked fucosyl residue is attached to the proximal GlcNAc residue of the di-N-acetylchitobiosyl unit; (iii) that the action of GlcNAc-transferase V, which catalyzes the attachment of the β-(1→6)-linked GlcNAc residue on the (1→6)-α-linked mannose (Man) arm, appears to be essential for polysialylation to occur on the core glycan chain is suggested by the fact that the Man residue α1→6-linked to the β-linked Man residue is invariably 2,6-di-O-substituted by the GlcNAc residue; (iv) both type 1 (Galβ1→3GlcNAc) and type 2 (Ga1β1→4 GlcNAc) sequences are present in the peripheral portion of the core glycan structure. An extended form of the type 2 chain, i.e. Galβ1→4GlcNAcβ1→3Galβ1→4GlcNAc, is also expressed on the (1→3)- and (1→6)-α-linked Man arms; (v) on average about 1.4 mol of sulfate is attached to the type 2 N-acetyllactosamine chain(s), where in the extended form the sulfate group is probably substituted at the O-3 position of the outmost GlcNAc residue, i.e. Galβ1→4(HSO<inf>3</inf>→3)GlcNAcβ1→3Galβ1→4GlcNAcβ1→Man. It is possible that the unusual structural features identified in this study might play a role in the initiation of polysialylation and our data should facilitate future research regarding the signals that control polysialylation.

DOI： 10.1074/jbc.271.51.32667

Space Plasma Observations-Observations of Solar-Terrestrial Environment Auroral Observations Using Satellites Reviewed

Broadband electrons observed by the DMSP satellites during storm-time substorms Reviewed

Shiokawa K, Yumoto K, Meng CI, Reeves G

GEOPHYSICAL RESEARCH LETTERS Vol. 23 ( 18 ) page： 2529 - 2532 1996.9

Quasi-periodic poleward motions of Sun-aligned auroral arcs in the high-latitude morning sector: A case study Reviewed

Shiokawa K, Yumoto K, Nishitani N, Hayashi K, Oguti T, McEwen DJ, Kiyama Y, Rich FJ, Mukai T

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 101 ( A9 ) page： 19789 - 19800 1996.9

SHIOKAWA Kazuo

Journal of plasma and fusion research Vol. 72 ( 1 ) page： 29-33 1996.1

Language：English Publishing type：Research paper (scientific journal)

It is important to monitor global auroral images which are the ionospheric projection of the plasma distribution in the magnetosphere. In the 1970's the auroral images were taken by using scanning photometers on board the ISIS-2 and DMSP satellites. One image was obtained for each polar pass of the satellites. In the 1980's, high time-resolution auroral images in UV wavelengthes were obtained by the KYOKKO. DE. VIKING, and AKEBONO satellites, using multichannel plate with CCD cameras. Fabri-Perot interferometer and monochromatic imaging photometers are also on board the DE satellites to make remote-sensing observations of the atmospheric dynamics through auroral emissions.

Quasi-periodic poleward motions of sun-alighed auroral arcs in the high-latitude morning sector: A case study Reviewed

Journal of Geophysical Research Vol. 101 page： A9 1996

Characteristics of low-latitude Pi 2 pulsations along the 210 degrees magnetic meridian Reviewed Open Access

Osaki H, Yumoto K, Fukao K, Shiokawa K, Menk FW, Fraser BJ

JOURNAL OF GEOMAGNETISM AND GEOELECTRICITY Vol. 48 ( 11 ) page： 1421-1430 1996

Auroral observations using automatic optical instruments: Relations with multiple Pi 2 magnetic pulsations Reviewed Open Access

Shiokawa K, Yumoto K, Tanaka Y, Osaki H, Sato M, Kato T, Kato Y, Sera M, Ikegami Y, Akasofu SI, Hayashi K, Oguti T, Kiyama Y

JOURNAL OF GEOMAGNETISM AND GEOELECTRICITY Vol. 48 ( 11 ) page： 1407 - 1419 1996

Modelling formation of new radiation belts and response to ULF oscillations following March 24, 1991 SSC Reviewed

MK Hudson, AD Kotelnikov, Li, X, JG Lyon, Roth, I, M Temerin, Wygant, JR, JB Blake, MS Gussenhoven, K Yumoto, K Shiokawa

WORKSHOP ON THE EARTH'S TRAPPED PARTICLE ENVIRONMENT ( 383 ) page： 119 - 127 1996

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AIP PRESS

The rapid formation of a new proton radiation belt at L similar or equal to 2.5 following the March 24, 1991 Storm Sudden Commencement (SSC) observed at the CRRES satellite is modelled using a relativistic guiding center test particle code. The new radiation belt formed on a time scale shorter than the drift period of eg. 20 MeV protons. The SSC is modelled by a bipolar electric field and associated compression and relaxation in the magnetic field, superimposed on a background dipole magnetic field. The source population consists of solar protons that populated the outer magnetosphere during the solar proton event that preceeded the SSC and trapped inner zone protons. The simulations show that both populations contribute to drift echoes in the 20-80 MeV range measured by the Aerospace instrument and in lower energy channels of the Protel instrument on CRRES, while primary contribution to the newly trapped population is from solar protons. Proton acceleration by the SSC differs from electron acceleration in two notable ways: different source populations contribute and nonrelativistic conservation of the first adiabatic invariant leads to greater energization of protons for a given decrease in L than for relativistic electrons. Model drift echoes, energy spectra and flux distribution in L at the time of injection compare well with CRRES observations. On the outbound pass, similar to 2 hours after the SSC, the broad spectral peak of the new radiation belt extends to higher energies (20 - 40 MeV) than immediately after formation. Electron flux oscillations observed at this later time are attributed to post-SSC impulses evident in ground magnetograms, while two minute period ULF oscillations also evident in CRRES field data appear to be cavity modes in the inner magnetosphere.

A low-latitude aurora observed at Rikubetsu (L=1.6) during the magnetic storm of September 13,1993 Reviewed

North/south asymmetry of sc/si magnetic variations observed along the 210 degrees magnetic meridian Reviewed Open Access

Yumoto K, Matsuoka H, Osaki H, Shiokawa K, Tanaka Y, Kitamura TI, Tachihara H, Shinohara M, Solovyev SI, Makarov GA, Vershinin EF, Buzevich AV, Manurung SL, Sobari O, Ruhimat M, Sukmadradjat, Morris RJ, Fraser BJ, Menk FW, Lynn KJW, Cole DG, Kennewell JA, Olson JV, Akasofu SI

JOURNAL OF GEOMAGNETISM AND GEOELECTRICITY Vol. 48 ( 11 ) page： 1333 - 1340 1996

A STATISTICAL STUDY OF THE MOTIONS OF AURORAL ARCS IN THE HIGH-LATITUDE MORNING SECTOR Reviewed

SHIOKAWA K, YUMOTO K, HAYASHI K, OGUTI T, MCEWEN DJ

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 100 ( A11 ) page： 21979 - 21985 1995.11

Shiokawa Kazuo, Yumoto Kiyohumi, Tanaka Yoshihito, Kiyama Yoshitaka, Kamide Yohsuke, Tokumaru Munetoshi

Proceedings of the NIPR Symposium on Upper Atmosphere Physics Vol. 8 page： 17 - 23 1995.5

Language：English Publishing type：Research paper (scientific journal) Publisher：National Institute of Polar Research

A low-latitude aurora was observed at Rikubetsu (L=1.6), Japan during the main phase of the moderate magnetic storm of September 13,1993. Although the sky at Rikubetsu was covered by thick clouds on this day, the aurora was identified as a significant enhancement in the 6300-A emission. It is likely that this aurora occurred in association with the expansion onset of an intense magnetospheric substorm, lasting approximately 1 hour. A notable point is that this aurora was observed during the moderate magnetic storm, indicating that low-latitude auroras are not always associated with intense magnetic storms. It is argued that the so-called Stable Auroral Red (SAR) arc and the substorm-associated low-latitude aurora should be distinguished in their production mechanisms, since the latter aurora must be accounted for in terms of substorm processes.