Faculty Profiles - SHIOKAWA, Kazuo

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