Faculty Profiles - SHIOKAWA, Kazuo

Papers - SHIOKAWA, Kazuo

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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

Scopus

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

Open Access

Scopus

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

Scopus

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

Scopus

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

Scopus

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

Open Access

CiNii Research

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

Scopus

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

Open Access

Scopus

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

2024.9

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

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

Scopus

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

Scopus

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

Open Access

Scopus

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

Scopus

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

Open Access

Scopus

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

Scopus

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

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Papers - SHIOKAWA, Kazuo