Faculty Profiles - SHIOKAWA, Kazuo

Papers - SHIOKAWA, Kazuo

Division display 61 - 80 of about 483 ／ All the affair displays >>

Statistical Analysis of Pc1 Wave Ducting Deduced From Swarm Satellites Reviewed

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

Web of Science

Scopus

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

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

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

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

Web of Science

Scopus

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

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

Web of Science

Scopus

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

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

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

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

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

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

Web of Science

Scopus

PubMed

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

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

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

Web of Science

Scopus

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

Web of Science

Scopus

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

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

Web of Science

Scopus

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

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

Web of Science

Scopus

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

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

Ionospheric Plasma Density Oscillation Related to EMIC Pc1 Waves Reviewed

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

Web of Science

Scopus

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

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

Web of Science

Scopus

PubMed

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

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

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

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

Web of Science

Scopus

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

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

Web of Science

Scopus

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

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

Web of Science

Scopus

　 PREV - NEXT 　

<SHIOKAWA, Kazuo>

Papers - SHIOKAWA, Kazuo