研究者詳細 - 塩川　和夫

論文 - 塩川　和夫

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Auroral Heating of Plasma Patches Due to High-Latitude Reconnection 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 12 ) 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

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

DOI： 10.1029/2021JA029657

Study of an Equatorward Detachment of Auroral Arc From the Oval Using Ground-Space Observations and the BATS-R-US-CIMI Model 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 12 ) 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

We present observations of an equatorward detachment of the auroral arc from the main oval and magnetically conjugate measurements made by the Arase satellite in the inner magnetosphere. The all-sky imager at Gakona (magnetic latitude = 63.6°N), Alaska, shows the detachment of the auroral arc in both red and green lines at local midnight (∼0130–0230 MLT) on 30 March 2017. The electron density derived from the Arase in-situ observations shows that this arc occurred outside the plasmapause. At the arc crossing, the electron flux of energies ∼0.1–2 keV is found to be locally enhanced at L∼4.3–4.5. We estimated auroral intensities for both red and green lines by using the Arase low-energy (0.1–19 keV) electron flux data. The peak latitude of the estimated intensity shows reasonably good correspondence with the observed intensity mapped at the ionospheric footprints of the Arase satellite. These findings indicate that the observed arc detachment at Gakona was associated with the localized enhancement of low-energy electrons (∼0.1–2 keV) at the inner edge of the electron plasma sheet. Further, we employ the simulation results of the Community Coordinated Modeling Center (CCMC), the BATS-R-US–CIMI 3-D MHD code to understand the conditions in the inner magnetosphere around the time of detachment. Although the simulation could not reproduce the lower-energy component responsible for the arc detachment, it successfully reproduced two earthward convection events at the lower radial distance (R) (R ≤ ∼4) around the time of arc detachment and the features of enhanced convection in similarity with the observations.

DOI： 10.1029/2020JA029080

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA029080

Multipoint Measurement of Fine-Structured EMIC Waves by Arase, Van Allen Probe A, and Ground Stations 査読有り

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

GEOPHYSICAL RESEARCH LETTERS 48 巻 ( 23 ) 2021年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Geophysical Research Letters

We examined the growth and propagation of fine-structured electromagnetic ion cyclotron (EMIC) waves related to time-varying density irregularities using multipoint measurement data observed by Arase, Van Allen Probe A, and two ground-based induction magnetometers (Gakona and Dawson) during a field line conjunction event on April 18, 2019. We analyzed the wave data obtained by the aforementioned spacecraft and stations, and found that the appearance of fine structures in the observed EMIC waves clearly coincided with the ambient electron density irregularities in the magnetosphere, which can cause periodic wave growth and waveguiding on their propagation. Furthermore, we found that the latitudinal widths of the EMIC wave activity region and the wave propagation duct were ∼185 km and less than 80 km at an auroral altitude of 100 km, respectively. We also found thermal ion heating ((Formula presented.) eV/q) during the EMIC wave activity.

DOI： 10.1029/2021GL096488

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021GL096488

Periodicities and Colors of Pulsating Auroras: DSLR Camera Observations From the International Space Station 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 10 ) 2021年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

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

DOI： 10.1029/2021JA029564

Isolated Proton Aurora Driven by EMIC Pc1 Wave: PWING, Swarm, and NOAA POES Multi-Instrument Observations 査読有り

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

GEOPHYSICAL RESEARCH LETTERS 48 巻 ( 18 ) 2021年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Geophysical Research Letters

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

DOI： 10.1029/2021GL095090

An experimental investigation into the possible connections between the zonal neutral wind speeds and equatorial plasma bubble drift velocities over the African equatorial region 査読有り

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

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 220 巻 2021年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Atmospheric and Solar-Terrestrial Physics

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

DOI： 10.1016/j.jastp.2021.105663

First Simultaneous Observation of a Night Time Medium-Scale Traveling Ionospheric Disturbance From the Ground and a Magnetospheric Satellite 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 9 ) 2021年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

Medium-scale traveling ionospheric disturbances (MSTIDs) are a phenomenon widely and frequently observed over the ionosphere from high to low latitudes. Night time MSTIDs are caused generally by the polarization electric field in the ionosphere. However, propagation of this polarization electric field to the magnetosphere has not yet been identified. Here, we report the first observation of the polarization electric field and associated density variations of a night time MSTID in the magnetosphere. The MSTID event was observed by an all-sky airglow imager at Gakona (geographical latitude: 62.39°N, geographical longitude: 214.78°E, magnetic latitude: 63.20°N), Alaska. The Arase satellite passed over the MSTID in the inner magnetosphere at 0530–0800 UT (2030–2300 LT) on November 3, 2018. This MSTID, observed in 630 nm airglow images, was propagating westward with a horizontal wavelength of ∼165 km, a north–south phase front, and a phase velocity of ∼80 m/s. The Arase satellite footprint on the ionosphere crossed the MSTID in the direction nearly perpendicular to the MSTID phase fronts. The electric field and electron density observed by the Arase satellite showed periodic variation associated with the MSTID structure with amplitudes of ∼2 mV/m and ∼150 cm−3, respectively. The electric field variations projected to the ionosphere are mainly in the east-west direction and are consistent with the direction of the polarization electric field expected from MSTID growth by E × B drift. This observation indicates that the polarization electric field associated with the MSTID in the ionosphere is projected onto the magnetosphere, causing plasma density fluctuations in the magnetosphere.

DOI： 10.1029/2020JA029086

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA029086

Multi-instrument study of longitudinal wave structures for plasma bubble seeding in the equatorial ionosphere 査読有り

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

EARTH AND PLANETARY PHYSICS 5 巻 ( 5 ) 頁： 368 - 377 2021年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Earth and Planetary Physics

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

DOI： 10.26464/epp2021047

PSTEP: project for solar-terrestrial environment prediction 査読有り国際誌

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

EARTH PLANETS AND SPACE 73 巻 ( 1 ) 2021年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Earth, Planets and Space

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

DOI： 10.1186/s40623-021-01486-1

太陽活動変動が地球環境を変えるか？

塩川和夫

学術の動向 26 巻 ( 8 ) 頁： 8_18 - 8_21 2021年8月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：公益財団法人日本学術協力財団

<p>　拡大する人類の宇宙利用の安全・安心な運用と太陽活動変動の地球気候への影響を理解・予測するために、国際学術会議傘下のSCOSTEPを中心としてPRESTO（変動する太陽地球結合系の予測可能性）プログラムが2020-2024年に推進されている。PRESTOでは、太陽・惑星間空間・ジオスペース、宇宙天気と地球大気、太陽活動とその気候影響、という3つの課題に対して国際共同研究が進められている。SCOSTEPは太陽地球系科学の発展のために、国際スクールやオンラインセミナー・講義、若手派遣事業を実施してきた。日本学術会議は日本の代表としてSCOSTEPに加盟し、分担金の拠出やSCOSTEPに対する国内対応の議論・情報交換を行ってきた。日本は、歴代のプログラムの国際会議を主催したり、SCOSTEP会長、副会長、理事やプログラム議長を輩出したりするなど、SCOSTEPの運営に大きく貢献している。</p>

DOI： 10.5363/tits.26.8_18

Spatial Evolution of Wave-Particle Interaction Region Deduced From Flash-Type Auroras and Chorus-Ray Tracing 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 7 ) 2021年7月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

In-situ observations of spatial variations of the wave-particle interaction region require a large number of satellite probes. As an alternative, flash-type auroras, a kind of pulsating aurora, driven by discrete chorus elements, can be used to investigate the interaction region with a high spatial resolution. We estimated the spatial extent of wave-particle interaction region from ground-based observations of flash aurora at Gakona (62.39°N, 214.78°E), Alaska at subauroral latitudes, and found that the auroral expansion was predominantly to the low-latitude side. The spatial displacement is thought to be caused by the propagation effects of chorus waves in the magnetosphere. Using ray tracing analysis to take into account chorus wave propagation, we reconstructed the spatiotemporal evolution of the volume emission rate and confirmed that the predominant expansion is toward the lower-latitude side in the ionosphere. This study shows that chorus wave propagation in the magnetosphere gives new insight for characterizing the transverse size (across the geomagnetic field line) of wave-particle interaction regions. The calculated spatial scale of the column auroral emission shows a correlation with the magnetic latitude of the resonance region at magnetic latitudes within 10° of the equatorial plane of the magnetosphere. Our results suggest that the spatial scale of a flash aurora is indirectly related to the chorus amplitude because the latitudinal range of the wave-particle interaction is important for the growth of wave amplitude.

DOI： 10.1029/2021JA029254

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JA029254

What controls the luminosity of polar cap airglow patches?: Implication from airglow measurements in Eureka, Canada in comparison with SuperDARN convection pattern 査読有り

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

POLAR SCIENCE 28 巻 2021年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Polar Science

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

DOI： 10.1016/j.polar.2020.100608

Influence of Zonal Wind Velocity Variation on Equatorial Plasma Bubble Occurrences Over Southeast Asia 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 5 ) 2021年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

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

DOI： 10.1029/2020JA028994

Simultaneous Observation of Two Isolated Proton Auroras at Subauroral Latitudes by a Highly Sensitive All-Sky Camera and Van Allen Probes 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 5 ) 2021年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

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

DOI： 10.1029/2020JA029078

Multi-Event Analysis of Plasma and Field Variations in Source of Stable Auroral Red (SAR) Arcs in Inner Magnetosphere During Non-Storm-Time Substorms 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 4 ) 2021年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

Stable auroral red (SAR) arcs are optical events with dominant 630.0-nm emission caused by low-energy electron heat flux into the topside ionosphere from the inner magnetosphere. SAR arcs are observed at subauroral latitudes and often occur during the recovery phase of magnetic storms and substorms. Past studies concluded that these low-energy electrons were generated in the spatial overlap region between the outer plasmasphere and ring-current ions and suggested that Coulomb collisions between plasmaspheric electrons and ring-current ions are more feasible for the SAR-arc generation mechanism rather than Landau damping by electromagnetic ion cyclotron waves or kinetic Alfvén waves. This work studies three separate SAR-arc events with conjunctions, using all-sky imagers and inner magnetospheric satellites (Arase and Radiation Belt Storm Probes [RBSP]) during non-storm-time substorms on December 19, 2012 (event 1), January 17, 2015 (event 2), and November 4, 2019 (event 3). We evaluated for the first time the heat flux via Coulomb collision using full-energy-range ion data obtained by the satellites. The electron heat fluxes due to Coulomb collisions reached ∼109 eV/cm2/s for events 1 and 2, indicating that Coulomb collisions could have caused the SAR arcs. RBSP-A also observed local enhancements of 7–20-mHz electromagnetic wave power above the SAR arc in event 2. The heat flux for the freshly detached SAR arc in event 3 reached ∼108 eV/cm2/s, which is insufficient to have caused the SAR arc. In event 3, local flux enhancement of electrons (<200 eV) and various electromagnetic waves were observed, these are likely to have caused the freshly detached SAR arc.

DOI： 10.1029/2020JA029081

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020JA029081

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

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

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS 215 巻 2021年4月

Development of research capacities in space weather: a successful international cooperation 査読有り

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

JOURNAL OF SPACE WEATHER AND SPACE CLIMATE 11 巻 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Space Weather and Space Climate

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

DOI： 10.1051/swsc/2021006

Magnetic Conjugacy of Pc1 Waves and Isolated Proton Precipitation at Subauroral Latitudes: Importance of Ionosphere as Intensity Modulation Region 査読有り

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

GEOPHYSICAL RESEARCH LETTERS 48 巻 ( 5 ) 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Geophysical Research Letters

Pc1 geomagnetic pulsations, equivalent to electromagnetic ion cyclotron waves in the magnetosphere, display a specific amplitude modulation, though the region of the modulation remains an open issue. To classify whether the amplitude modulation has a magnetospheric or ionospheric origin, an isolated proton aurora (IPA), which is a proxy of Pc1 wave-particle interactions, is compared with the associated Pc1 waves for a geomagnetic conjugate pair, Halley Research Base in Antarctica and Nain in Canada. The temporal variation of an IPA shows a higher correlation coefficient (0.88) with Pc1 waves in the same hemisphere than that in the opposite hemisphere. This conjugate observation reveals that the classic cyclotron resonance is insufficient to determine the amplitude modulation. We suggest that direct wave radiation from the ionospheric current by IPA should also contribute to the amplitude modulation.

DOI： 10.1029/2020GL091384

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020GL091384

A review of the SCOSTEP's 5-year scientific program VarSITI-Variability of the Sun and Its Terrestrial Impact 査読有り

Shiokawa Kazuo, Georgieva Katya

PROGRESS IN EARTH AND PLANETARY SCIENCE 8 巻 ( 1 ) 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Progress in Earth and Planetary Science

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

DOI： 10.1186/s40645-021-00410-1

GPS Scintillations and TEC Variations in Association With a Polar Cap Arc 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 126 巻 ( 3 ) 2021年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Geophysical Research: Space Physics

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

DOI： 10.1029/2020JA028968

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