研究者詳細 - 塩川　和夫

論文 - 塩川　和夫

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Three-Dimensional Fourier Analysis of the Phase Velocity Distributions of Mesospheric and Ionospheric Waves Based on Airglow Images Collected Over 10 Years: Comparison of Magadan, Russia, and Athabasca, Canada 査読有り

Tsuchiya Satoshi, Shiokawa Kazuo, Fujinami Hatsuki, Otsuka Yuichi, Nakamura Takuji, Connors Martin, Schofield Ian, Shevtsov Boris, Poddelskiy Igor

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 124 巻 ( 10 ) 頁： 8110 - 8124 2019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 studied atmospheric gravity waves (AGWs) and nighttime medium-scale traveling ionospheric disturbances (MSTIDs) using a three-dimensional spectral analysis technique for airglow images at wavelengths of 557.7 nm (altitude: 90–100 km for AGWs) and 630.0 nm (200–300 km for MSTIDs), obtained from Athabasca (ATH), Canada (55°N, 247°E, 2005–2017), and Magadan (MGD), Russia (60°N, 151°E, 2008–2017), over 10–13 years. The AGW propagation direction in summer was from northwestward to northward in ATH and northeastward in MGD with phase speeds of 20–60 m/s. In winter at ATH, they are more omnidirectional with weak preference from northwestward to southward with a speed less than 40 m/s, while another weaker power exists from northeastward to southeastward from 70 to 120 m/s. In winter at MGD, there was no dominant direction in the phase-velocity spectra with spectral power an order smaller than ATH. We suggest that these AGW characteristics were caused by wind filtering and intensity and locations of tropospheric sources. The MSTIDs at ATH propagated southwestward in spring and winter and northeastward in summer and fall. The MSTIDs at MGD propagated northeastward, eastward, and westward in spring, fall, and winter, respectively, with weaker power than that at ATH. The phase speeds are mostly less than 100 m/s except for fall. The propagation direction tends to change from south-southwestward in the evening to north-northeastward after the midnight at both ATH and MGD. We discuss possible reasons for these MSTID characteristics at high latitudes based on Perkins and E-F coupling instabilities, high-latitude plasma convection, and thermospheric neutral winds.

DOI： 10.1029/2019JA026783

Mesoscale Convection Structures Associated With Airglow Patches Characterized Using Cluster-Imager Conjunctions 査読有り

Goodwin L. V, Nishimura Y., Zou Y., Shiokawa K., Jayachandran P. T.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 124 巻 ( 9 ) 頁： 7513 - 7532 2019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

Polar cap ionospheric plasma flow studies often focus on large-scale averaged properties and neglect the mesoscale component. However, recent studies have shown that mesoscale flows are often found to be collocated with airglow patches. These mesoscale flows are typically a few hundred meters per second faster than the large-scale background and are associated with major auroral intensifications when they reach the poleward boundary of the nightside auroral oval. Patches often also contain ionospheric signatures of enhanced field-aligned currents and localized electron flux enhancements, indicating that patches are associated with magnetosphere-ionosphere coupling on open field lines. However, magnetospheric measurements of this coupling are lacking, and it has not been understood what the magnetospheric signatures of patches on open field lines are. The work presented here explores the magnetospheric counterpart of patches and the role these structures have in plasma transport across the open field-line region in the magnetosphere. Using red-line emission measurements from the Resolute Bay Optical Mesosphere Thermosphere Imager, and magnetospheric measurements made by the Cluster spacecraft, conjugate events from 2005 to 2009 show that lobe measurements on field lines connected to patches display (1) electric field enhancements, (2) Region 1 sense field-aligned currents, (3) field-aligned enhancements in soft electron flux, (4) downward Poynting fluxes, and (5) in some cases enhancements in ion flux, including ion outflows. These observations indicate that patches highlight a localized fast flow channel system that is driven by the magnetosphere and propagates from the dayside to the nightside, most likely being initiated by enhanced localized dayside reconnection.

DOI： 10.1029/2019JA026611

Thermospheric wind variations observed by a Fabry-Perot interferometer at Tromso, Norway, at substorm onsets 査読有り

Xu Heqiucen, Shiokawa Kazuo, Oyama Shin-ichiro, Otsuka Yuichi

EARTH PLANETS AND SPACE 71 巻 ( 1 ) 2019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

Energy input from the magnetosphere during substorms can strongly affect the high-latitude thermosphere. The ionospheric current caused by thermospheric wind variations may also provide a feedback to the magnetosphere. In this study, we investigate the characteristics of high-latitude thermospheric wind variations at local substorm onsets at Tromsø, Norway, as well as the possibility of such feedback mechanism. A Fabry–Perot interferometer (FPI) at Tromsø provided wind measurements estimated from the Doppler shift of red-line emission (630.0 nm) of aurora and airglow. We analyzed wind data in 2009 with a time resolution of ~ 13 min. We first carefully identified the onset times of isolated local substorms at Tromsø and extracted four wind measurements from red-line emission. All these events showed increases of eastward components at local substorm onsets. For northward components, these events showed decreases except for those at midnight. The observed wind variations at local substorm onsets were less than 49 m/s. These values are much smaller than the typical plasma convection speed in the auroral zone. We speculate that the ionospheric current caused by thermospheric wind variations at local substorm onsets does not provide strong feedback to the development of substorm expansion phase in the magnetotail. We discuss the possible causes of these wind variations in the context of plasma convection, diurnal tides, and arc-associated electric field.

DOI： 10.1186/s40623-019-1072-0

Multi-instrument Observation of Nonlinear EMIC-Driven Electron Precipitation at sub-MeV Energies 査読有り

Hendry A. T., Santolik O., Kletzing C. A., Rodger C. J., Shiokawa K., Baishev D.

GEOPHYSICAL RESEARCH LETTERS 46 巻 ( 13 ) 頁： 7248 - 7257 2019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：Geophysical Research Letters

In recent years, experimental results have consistently shown evidence of electromagnetic ion cyclotron (EMIC) wave-driven electron precipitation down to energies as low as hundreds of keV. However, this is at odds with the limits expected from quasi-linear theory. Recent analysis using nonlinear theory has suggested energy limits as low as hundreds of keV, consistent with the experimental results, although to date this has not been experimentally verified. In this study, we present concurrent observations from Polar-orbiting Operational Environmental Satellite, Radiation Belt Storm Probes, Global Positioning System, and ground-based instruments, showing concurrent EMIC waves and sub–MeV electron precipitation, and a global dropout in electron flux. We show through test particle simulation that the observed waves are capable of scattering electrons as low as hundreds of keV into the loss cone through nonlinear trapping, consistent with the experimentally observed electron precipitation.

DOI： 10.1029/2019GL082401

EMIC Waves Converted From Equatorial Noise Due to <i>M/Q</i>=2 Ions in the Plasmasphere: Observations From Van Allen Probes and Arase 査読有り

Miyoshi Y., Matsuda S., Kurita S., Nomura K., Keika K., Shoji M., Kitamura N., Kasahara Y., Matsuoka A., Shinohara I., Shiokawa K., Machida S., Santolik O., Boardsen S. A., Horne R. B., Wygant J. F.

GEOPHYSICAL RESEARCH LETTERS 46 巻 ( 11 ) 頁： 5662 - 5669 2019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：Geophysical Research Letters

Equatorial noise (EN) emissions are observed inside and outside the plasmapause. EN emissions are referred to as magnetosonic mode waves. Using data from Van Allen Probes and Arase, we found conversion from EN emissions to electromagnetic ion cyclotron (EMIC) waves in the plasmasphere and in the topside ionosphere. A low-frequency part of EN emissions becomes EMIC waves through branch splitting of EN emissions, and the mode conversion from EN to EMIC waves occurs around the frequency of M/Q = 2 (deuteron and/or alpha particles) cyclotron frequency. These processes result in plasmaspheric EMIC waves. We investigated the ion composition ratio by characteristic frequencies of EN emissions and EMIC waves and obtained ion composition ratios. We found that the maximum composition ratio of M/Q = 2 ions is ~10% below 3,000 km. The quantitative estimation of the ion composition will contribute to improving the plasma model of the deep plasmasphere and the topside ionosphere.

DOI： 10.1029/2019GL083024

Comprehensive Study of Low-Latitude Pi2 Pulsations Using Observations From Multisatellite Swarm Mission and Global Network of Ground Observatories 査読有り

Thomas Neethal, Shiokawa Kazuo, Vichare Geeta

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 124 巻 ( 3 ) 頁： 1966 - 1991 2019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

To understand the spatial features of low-latitude Pi2 (6.6–25 mHz) pulsations, a comprehensive study is carried out for the first time using magnetic field measurements from a global network of low-latitude ground stations (Mlat: ± 2° − 51°) and the Swarm multisatellites located simultaneously at day and night local times. We have investigated 1-year data from 2014 and found 15 Pi2 events with coherent oscillations at satellite and ground. The Pi2 oscillations in the compressional, toroidal, and poloidal components at satellite and H, D, and Z components at ground are investigated by estimating its coherence, amplitude, and cross phase with respect to midnight ground H variations. The analogous pairs of magnetic field components (satellite compressional with ground H and satellite toroidal with ground D) above and below the ionosphere are found to have identical phase during night and opposite phase during day, indicating the magnetospheric and ionospheric sources for nighttime and daytime Pi2s, respectively. During nighttime, Pi2 oscillations identified in the poloidal component are found to oscillate in phase (out of phase) in the Southern (Northern) Hemisphere. At ground, the phase and amplitude of H showed significant change near the dawn terminator, whereas H oscillates mostly in phase with respect to midnight ground H at other local times. The oscillations in D component have phase reversal near midnight, dawn, dusk, and noon meridians with opposite hemispheres having opposite phase. These Pi2 characteristics observed globally at ground and at the topside ionosphere suggest that the sources for nighttime and daytime low-latitude Pi2s are oscillating field-aligned currents and ionospheric currents, respectively.

DOI： 10.1029/2018JA026094

Observations of Low-Latitude Traveling Ionospheric Disturbances by a 630.0-nm Airglow Imager and the CHAMP Satellite Over Indonesia 査読有り国際誌

Moral Aysegul Ceren, Shiokawa Kazuo, Suzuki Shin, Liu Huixin, Otsuka Yuichi, Yatini Clara Yoko

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 124 巻 ( 3 ) 頁： 2198 - 2212 2019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

We report the first comparison of ground and satellite measurements of low-latitude traveling ionospheric disturbances (TIDs). Three TID events were simultaneously observed by a 630.0-nm airglow imager and the CHAllenging Minisatellite Payload (CHAMP) satellite at Kototabang, Indonesia (geographic coordinates: 0.2° S, 100.3° E, geomagnetic latitude: 10.6° S). In 630.0-nm airglow images of all three events, there are clear southward-moving structures. Events 1 and 2 are a single pulse with horizontal scales of ∼500–1,000 km. Event 3 shows five wave fronts with a horizontal scale size of 500–1,000 km. All three TIDs are medium-scale TIDs. Horizontal wavelengths of both airglow intensity at an average emission altitude of 250 km and CHAMP neutral density variations measured at 400 km are estimated by fitting a sinusoidal function to the observed data. The estimated horizontal wavelengths for airglow and neutral density data are 1,031 and 880 km for event 1 and 560 and 420 km for event 3, respectively. These values between airglow and CHAMP are comparable, suggesting both instruments are observing the same wave. For event 1, the CHAMP electron density mapped along the geomagnetic field line onto the airglow altitude does not show wave structure similar to the airglow variation. For events 2 and 3, the plasma density did not show wavy structures similar to the waves seen in the airglow image and CHAMP neutral density. These results suggest that the TIDs observed in airglow images are not caused by ionospheric plasma instability but by gravity waves in the thermosphere.

DOI： 10.1029/2018JA025634

Spatial Gradients in Geomagnetic Storm Time Currents Observed by Swarm Multispacecraft Mission 査読有り

Vichare Geeta, Thomas Neethal, Shiokawa Kazau, Bhaskar Ankush, Sinha Ashwini Kumar

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 124 巻 ( 2 ) 頁： 982 - 995 2019年2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 paper presents a comprehensive study of geomagnetic storm time currents using magnetic field recorded by multispacecraft polar-orbiting mission, Swarm. During geomagnetic storm period, the magnetic field variations obtained after removing the internal geomagnetic field and quiet time contributions can be considered as a proxy for storm time currents and are found to follow the temporal profile of Dst index very closely. These variations at the equatorial crossings recorded by multiple-spacecraft are used to estimate the Dst values and are found to have a good match with the ground-based Dst index. The average deviation between these two is around 4–13%. We have estimated the asymmetry by taking the difference between the magnetic field variations at two local time sectors separated by 12 hr. The estimated asymmetry shows a good match with the AsyH-index, especially when satellite traverses in the dawn-dusk sector. In general, the magnetic field variations are stronger in the night-to-dusk sector than day-to-dawn sector, which could be due to the larger pressure-gradients near night-to-dusk caused by ion movements. The important advantage of Swarm mission is that it provides an opportunity to investigate the longitudinal gradients in the storm time magnetic fields. It is observed that in general, the gradients are stronger during the main phase of the storm, centered near the equator with a latitudinal width of ~20–30° in both the hemispheres, and are supportive to the scenario of particle-injection from the magnetotail. The stronger gradients are observed at higher latitudes (~40°) during the episodes of substorms and might be associated with the ionospheric/field-aligned currents.

DOI： 10.1029/2018JA025692

Transient ionization of the mesosphere during auroral breakup: Arase satellite and ground-based conjugate observations at Syowa Station 査読有り

Kataoka Ryuho, Nishiyama Takanori, Tanaka Yoshimasa, Kadokura Akira, Uchida Herbert Akihito, Ebihara Yusuke, Ejiri Mitsumu K., Tomikawa Yoshihiro, Tsutsumi Masaki, Sato Kaoru, Miyoshi Yoshizumi, Shiokawa Kazuo, Kurita Satoshi, Kasahara Yoshiya, Ozaki Mitsunori, Hosokawa Keisuke, Matsuda Shoya, Shinohara Iku, Takashima Takeshi, Sato Tatsuhiko, Mitani Takefumi, Hori Tomoaki, Higashio Nana

EARTH PLANETS AND SPACE 71 巻 ( 1 ) 頁： 9 2019年1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

Transient mesospheric echo in the VHF range was detected at an altitude of 65–70 km during the auroral breakup that occurred from 2220 to 2226 UT on June 30, 2017. During this event, the footprint of the Arase satellite was located within the field of view of the all-sky imagers at Syowa Station in the Antarctic. Auroral observations at Syowa Station revealed the dominant precipitation of relatively soft electrons during the auroral breakup. A corresponding spike in cosmic noise absorption was also observed at Syowa Station, while the Arase satellite observed a flux enhancement of > 100 keV electrons and a broadband noise without detecting chorus waves or electromagnetic ion cyclotron waves. A general-purpose Monte Carlo particle transport simulation code was used to quantitatively evaluate the ionization in the middle atmosphere. Results of this study indicate that the precipitation of energetic electrons of > 100 keV, rather than X-rays from the auroral electrons, played a dominant role in the transient and deep (65–70 km) mesospheric ionization during the observed auroral breakup.[Figure not available: see fulltext.].

DOI： 10.1186/s40623-019-0989-7

Visualization of rapid electron precipitation via chorus element wave-particle interactions 査読有り

Ozaki Mitsunori, Miyoshi Yoshizumi, Shiokawa Kazuo, Hosokawa Keisuke, Oyama Shin-ichiro, Kataoka Ryuho, Ebihara Yusuke, Ogawa Yasunobu, Kasahara Yoshiya, Yagitani Satoshi, Kasaba Yasumasa, Kumamoto Atsushi, Tsuchiya Fuminori, Matsuda Shoya, Katoh Yuto, Hikishima Mitsuru, Kurita Satoshi, Otsuka Yuichi, Moore Robert C., Tanaka Yoshimasa, Nose Masahito, Nagatsuma Tsutomu, Nishitani Nozomu, Kadokura Akira, Connors Martin, Inoue Takumi, Matsuoka Ayako, Shinohara Iku

NATURE COMMUNICATIONS 10 巻 ( 1 ) 頁： 257 2019年1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：Nature Communications

Chorus waves, among the most intense electromagnetic emissions in the Earth’s magnetosphere, magnetized planets, and laboratory plasmas, play an important role in the acceleration and loss of energetic electrons in the plasma universe through resonant interactions with electrons. However, the spatial evolution of the electron resonant interactions with electromagnetic waves remains poorly understood owing to imaging difficulties. Here we provide a compelling visualization of chorus element wave–particle interactions in the Earth’s magnetosphere. Through in-situ measurements of chorus waveforms with the Arase satellite and transient auroral flashes from electron precipitation events as detected by 100-Hz video sampling from the ground, Earth’s aurora becomes a display for the resonant interactions. Our observations capture an asymmetric spatial development, correlated strongly with the amplitude variation of discrete chorus elements. This finding is not theoretically predicted but helps in understanding the rapid scattering processes of energetic electrons near the Earth and other magnetized planets.

DOI： 10.1038/s41467-018-07996-z

PRELIMINARY RESULTS OF SIMULTANEOUS RECORDING OF AURORAL AND GEOMAGNETIC PULSATIONS AT THE ISTP SB RAS STATION ISTOK 査読有り

Beletskii A. B., Rakhmatulin R. A., Syrenova T. Ye, Vasilev R. V., Mikhalev A. V, Pashinin A. Yu, Shiokawa K., Nishitani N.

SOLAR-TERRESTRIAL PHYSICS 5 巻 ( 2 ) 頁： 39 - 44 2019年

Preliminary results of simultaneous recording of auroral and geomagnetic pulsations at the ISTP SB RAS station Istok 査読有り Open Access

Beletskii A.B., Rakhmatulin R.A., Syrenova T.Y., Vasilev R.V., Mikhalev A.V., Pashinin A.Y., Shiokawa K., Nishitani N.

Solnecno-Zemnaa Fizika 5 巻 ( 2 ) 頁： 43 - 48 2019年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Solnecno-Zemnaa Fizika

The paper presents the results on first synchronous observations of variations in auroral luminosity and geomagnetic field, made with high temporal resolution at the ISTP SB RAS high-latitude station Istok (70° N, 88° E) in September–December 2018. Auroras were recorded with all-sky camera, pulsations in the auroras were recorded by a photometer in four spectral ranges with silicon photomultipliers. Continuous monitoring of geomagnetic pulsations was performed using a LEMI-30 three-component induction magnetometer. Both synchronous bursts of auroras and magnetic field pulsations, as well as disturbances of auroras, not accompanied by disturbances in the geomagnetic field, were observed. We note that the photometer clearly recorded short-period (~20 min) variations in in auroral luminosity. At the same time, some instability of the photometer signal level occurred at sufficiently long time intervals. In the photometer data, there are powerful signal bursts, probably of a hardware nature. Nevertheless, the temporary distribution analysis of the registration moments (registration frequency) of signal bursts indicates the possible dependence of the burst registration frequency on the geomagnetic activity level.

DOI： 10.12737/szf-52201906

Spatiotemporal development of pulsating auroral patch associated with discrete chorus elements: Arase and PWING observations 査読有り

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年

Temporal and Spatial Correspondence of Pc1/EMIC Waves and Relativistic Electron Precipitations Observed With Ground-Based Multi-Instruments on 27 March 2017 査読有り

Hirai A., Tsuchiya F., Obara T., Kasaba Y., Katoh Y., Misawa H., Shiokawa K., Miyoshi Y., Kurita S., Matsuda S., Connors M., Nagatsuma T., Sakaguchi K., Kasahara Y., Kumamoto A., Matsuoka A., Shoji M., Shinohara I., Albert J. M.

GEOPHYSICAL RESEARCH LETTERS 45 巻 ( 24 ) 頁： 13182 - 13191 2018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：Geophysical Research Letters

Electromagnetic ion cyclotron (EMIC) waves potentially cause precipitation loss of relativistic electrons from the outer radiation belt to the atmosphere through pitch angle scattering. However, the direct evidence of each EMIC wave element and burst of precipitation has not yet been reported. Here we show the temporal and spatial correspondence of the EMIC waves with relativistic electron precipitation (REP) during the geomagnetic storm of 27 March 2017. EMIC waves were observed at several stations in North America. REP was detected as a decrease of subionospheric radio amplitudes observed at Athabasca, Canada. When isolated proton aurora, observed at Athabasca, appeared on the radio propagation path, we found a good correspondence between the temporal variations of REP and EMIC waves, and REP preceded EMIC waves by 24 s. This time lag is consistent with the travel time difference between relativistic electrons and EMIC waves from the magnetospheric equatorial plane to the ionosphere.

DOI： 10.1029/2018GL080126

Electrostatic Electron Cyclotron Harmonic Waves as a Candidate to Cause Pulsating Auroras 査読有り

Fukizawa M., Sakanoi T., Miyoshi Y., Hosokawa K., Shiokawa K., Katoh Y., Kazama Y., Kumamoto A., Tsuchiya F., Miyashita Y., Tanaka Y-M., Kasahara Y., Ozaki M., Matsuoka A., Matsuda S., Hikishima M., Oyama S., Ogawa Y., Kurita S., Fujii R.

GEOPHYSICAL RESEARCH LETTERS 45 巻 ( 23 ) 頁： 12661 - 12668 2018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：Geophysical Research Letters

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

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 45 巻 ( 23 ) 頁： 12720 - 12729 2018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：Geophysical Research Letters

There has been increasing evidence for pitch angle scattering of relativistic electrons by electromagnetic ion cyclotron (EMIC) waves. Theoretical studies have predicted that the loss time scale of MeV electrons by EMIC waves can be very fast, suggesting that MeV electron fluxes rapidly decrease in association with the EMIC wave activity. This study reports on a unique event of MeV electron loss induced by EMIC waves based on Arase, Van Allen Probes, and ground-based network observations. Arase observed a signature of MeV electron loss by EMIC waves, and the satellite and ground-based observations constrained spatial-temporal variations of the EMIC wave activity during the loss event. Multisatellite observation of MeV electron fluxes showed that ~2.5-MeV electron fluxes substantially decreased within a few tens of minutes where the EMIC waves were present. The present study provides an observational estimate of the loss time scale of MeV electrons by EMIC waves.

DOI： 10.1029/2018GL080262

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2018GL080262

Large-Scale Ducting of Pc1 Pulsations Observed by Swarm Satellites and Multiple Ground Networks 査読有り

Kim Hyangpyo, Hwang Junga, Park Jaeheung, Miyashita Yukinaga, Shiokawa Kazuo, Mann Ian R., Raita Tero, Lee Jaejin

GEOPHYSICAL RESEARCH LETTERS 45 巻 ( 23 ) 頁： 12703 - 12712 2018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：Geophysical Research Letters

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 the Recovery Phase of a Substorm on 27 March 2017 査読有り

Tsuchiya F., Hirai A., Obara T., Misawa H., Kurita S., Miyoshi Y., Shiokawa K., Connors M., Ozaki M., Kasahara Y., Kumamoto A., Kasaba Y., Matsuoka A., Shoji M., Shinohara I.

GEOPHYSICAL RESEARCH LETTERS 45 巻 ( 23 ) 頁： 12651 - 12660 2018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：Geophysical Research Letters

Recent studies suggest that electrons with energies up to several hundred keV precipitate into the atmosphere associated with pulsating aurora (PsA). It is debated the highest energy of precipitating electrons associated with PsA. Here we report for the first time that the energy extends to relativistic energies. PsA was observed by THEMIS all-sky imagers during a substorm that occurred on 27 March 2017. Energetic electron precipitation was detected by very low frequency subionospheric propagation. We found similar time variations between the auroral intensity and perturbation of the received radio signal intensity when the PsA occurred on the radio path. The perturbation showed a short recovery time of ~2 s. The recovery time indicates relaxation from ionospheric modification due to energetic electron precipitation and depends on the stopping altitude of the electrons. The recovery time required a stopping altitude of 50–60 km and indicates that the PsA is accompanied by relativistic electron precipitation.

DOI： 10.1029/2018GL080222

The ARASE (ERG) magnetic field investigation 査読有り

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 70 巻 ( 1 ) 2018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：Earth, Planets and Space

© 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 査読有り

Perwitasari Septi, Nakamura Takuji, Kogure Masaru, Tomikawa Yoshihiro, Ejiri Mitsumu K., Shiokawa Kazuo

ANNALES GEOPHYSICAE 36 巻 ( 6 ) 頁： 1597 - 1605 2018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：Annales Geophysicae

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- S, 40- E); Shigaraki, Japan (35- N, 136- E); and Tomohon, Indonesia (1- N, 122- 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 < 50ms-1 at the Syowa Station and east-southeastward with a phase speed of up to - 80ms-1 in Shigaraki. The day-to-day variation in Tomohon is too strong to discuss average characteristics; however, a phase speed of up to - 100ms-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

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