Faculty Profiles - SHIOKAWA, Kazuo

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

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

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

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