研究者詳細 - 塩川　和夫

論文 - 塩川　和夫

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Observation of Source Plasma and Field Variations of a Substorm Brightening Aurora at <i>L</i> ∼ 6 by a Ground-Based Camera and the Arase Satellite on 12 October 2017 査読有り

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

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 127 巻 ( 11 ) 2022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：Journal of Geophysical Research: Space Physics

Auroral brightening is one of the most common phenomena that occur during substorm onset and is usually recognized as a projection of the substorm-associated magnetospheric plasma dynamics to the ionosphere. However, electromagnetic fields and plasma features associated with the substorm brightening arc have not been well understood. In this study, we present a comprehensive observation of the source plasma and field variations of a substorm brightening aurora in the inner magnetosphere. We performed a unique conjugate observation of a substorm brightening auroral arc observed by a ground-based camera and by the Arase satellite in the magnetospheric source region at L ∼ 6. The event was observed at Tromsø (69.6°N, 19.2°E), Norway, on 12 October 2017. The brightening arc indicates east-west structures with longitudinal scales of ∼0.5°–2.0°. Field-aligned bi-directional electrons with an energy range between 66 and 1,800 eV were detected by the satellite, simultaneously with the appearance of the brightening arc in the camera. These electrons were probably supplied from the auroral brightening region in the ionosphere, indicating that the satellite was on the same field line of the brightening aurora. The magnetic and electric field data show characteristic fluctuations and earthward Poynting flux around the time that the satellite crossed the aurora. Anti-phase oscillations between the thermal pressure and the magnetic pressure are also reported. Based on these observations, we suggest the possibility that a ballooning instability occurred in the source region of the substorm brightening arc in the inner magnetosphere at L ∼ 6.

DOI： 10.1029/2021JA030072

Thermospheric wind response to a sudden ionospheric variation in the trough: event at a pseudo-breakup during geomagnetically quiet conditions 査読有り

Oyama Shin-ichiro, Vanhamaki Heikki, Cai Lei, Aikio Anita, Rietveld Michael, Ogawa Yasunobu, Raita Tero, Kellinsalmi Mirjam, Kauristie Kirsti, Kozelov Boris, Shinbori Atsuki, Shiokawa Kazuo, Tsuda Takuo T., Sakanoi Takeshi

EARTH PLANETS AND SPACE 74 巻 ( 1 ) 頁： 154 2022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：Earth, Planets and Space

The thermospheric wind response to a sudden westward turning of the ion velocity at a high latitude was studied by analyzing data obtained with a Fabry–Perot interferometer (FPI; 630 nm), Dynasonde, and Swarm A & C satellites during a conjunction event. The event occurred during a geomagnetically quiet period (Kp = 0 +) through the night, but some auroral activity occurred in the north. The collocated FPI and Dynasonde measured the thermospheric wind (U) and ionospheric plasma velocity (V), respectively, in the F region at the equatorward trough edge. A notable scientific message from this study is the possible role of thermospheric wind in the energy dissipation process at F-region altitude. The FPI thermospheric wind did not instantly follow a sudden V change due to thermospheric inertia in the F region. At a pseudo-breakup during the event, V suddenly changed direction from eastward to westward within 10 min. U was concurrently accelerated westward, but its development was more gradual than that of V, with U remaining eastward for a while after the pseudo-breakup. The delay of U is attributed to the thermospheric inertia. During this transition interval, U∙V was negative, which would result in more efficient generation of frictional heating than the positive U∙V case. The sign of U∙V, which is related to the relative directions of the neutral wind and plasma drift, is important because of its direct impact on ion-neutral energy exchange during collisions. This becomes especially important during substorm events, where rapid plasma velocity changes are common. The sign of U∙V may be used as an indicator to find the times and locations where thermospheric inertia plays a role in the energy dissipation process. Graphical Abstract: [Figure not available: see fulltext.]

DOI： 10.1186/s40623-022-01710-6

Localized mesospheric ozone destruction corresponding to isolated proton aurora coming from Earth's radiation belt 査読有り国際誌

Ozaki Mitsunori, Shiokawa Kazuo, Kataoka Ryuho, Mlynczak Martin, Paxton Larry, Connors Martin, Yagitani Satoshi, Hashimoto Shion, Otsuka Yuichi, Nakahira Satoshi, Mann Ian

SCIENTIFIC REPORTS 12 巻 ( 1 ) 頁： 16300 - 16300 2022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：Scientific Reports

Relativistic electron precipitation (REP) from the Earth’s radiation belt plays an important role in mesospheric ozone loss as a connection between space weather and the climate system. However, the rapid (tens of minutes) destruction of mesospheric ozone directly caused by REP has remained poorly understood due to the difficulty of recognizing its location and duration. Here we show a compelling rapid correspondence between localized REP and ozone destruction during a specific auroral phenomenon, the called an isolated proton aurora (IPA). The IPA from the Earth’s radiation belt becomes an important spatial and temporal proxy of REP, distinct from other auroral phenomena, and allowing visualizing micro-ozone holes. We found ozone destruction of as much as 10–60% within 1.5 h of the initiation of IPA. Electromagnetic ion cyclotron waves in the oxygen ion band observed as the driver of REP likely affect through resonance with mainly ultra-relativistic (> 2 mega-electron-volts) energy electrons. The rapid REP impact demonstrates its crucial role and direct effect on regulating the atmospheric chemical balance.

DOI： 10.1038/s41598-022-20548-2

Three-Dimensional Fourier Analysis of Atmospheric Gravity Waves and Medium-Scale Traveling Ionospheric Disturbances Observed in Airglow Images in Hawaii Over Three Years 査読有り

Naito Hideto, Shiokawa Kazuo, Otsuka Yuichi, Fujinami Hatsuki, Tsuboi Takuma, Sakanoi Takeshi, Saito Akinori, Nakamura Takuji

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 127 巻 ( 10 ) 2022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

Three-dimensional Fourier spectral analysis of airglow images is a useful technique to provide propagation characteristics of atmospheric gravity waves (AGWs) in the mesopause region and medium-scale traveling ionospheric disturbances (MSTIDs) in the thermosphere observed at emission wavelengths of 557.7 nm (altitudes: 90–100 km for AGWs) and 630.0 nm (200–300 km for MSTIDs). However, a statistical study of spectral analysis of airglow images over years has not been done yet at Hawaii. Here, we report the first spectral analysis of AGWs and MSTIDs using airglow images obtained at Haleakala (20.71°N, 203.74°E), Hawaii, during the three years from 2013 to 2016. The power spectral density (PSD) of AGWs tends to be larger toward north to northeast in summer and from north to west and southward in winter. The eastward (summer) and westward (winter) preferences are consistent with a wind-filtering mechanism of AGWs by a mesospheric jet. Some correspondence is found between the locations of tropospheric convection activities and AGW propagation directions, suggesting that these mesospheric AGWs are originated from the troposphere. The PSDs of MSTIDs are larger in solstice than in equinox. This PSD enhancement in solstice is consistent with a sporadic-E (Es) layer occurrence in either northern or southern hemisphere, suggesting that the MSTIDs over Hawaii could be caused by a coupling process between the Perkins and Es layer instabilities. A small correlation was found between the PSDs of AGWs in the mesopause region and the PSDs of MSTIDs, suggesting that the MSTIDs are partly caused by AGWs from the mesopause region.

DOI： 10.1029/2022JA030346

Multi-Event Study of Simultaneous Observations of Isolated Proton Auroras at Subauroral Latitudes Using Ground All-Sky Imagers and the Van Allen Probes 査読有り

Nakamura Kohki, Shiokawa Kazuo, Nose Masahito, Nagatsuma Tsutomu, Sakaguchi Kaori, Spence Harlan, Reeves Geoff, Funsten Herbert O., MacDowall Robert, Smith Charles, Wygant John, Bonnell John, Mann Ian R.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 127 巻 ( 9 ) 2022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

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. Thus, an IPA is the ionospheric projection of the spatial and temporal variation of wave-particle interaction regions in the magnetosphere. In this study, we conducted unique multi-event analysis of simultaneous observations of IPAs and their source regions on 22 April, 7 September, and 22 March 2018, using all-sky imagers at subauroral latitudes and the Van Allen Probes. When the satellite footprint passed over the IPAs associated with ground Pc1 geomagnetic pulsations, locally generated He+-band EMIC waves with the same frequencies as the ground Pc1 pulsations were observed in all events. The IPAs and EMIC waves had comparable narrow widths in the latitudinal direction. The EMIC waves appeared during the rapid enhancement of the ring current proton flux at energy range of ∼10–50 keV, while they disappeared at the rapid decrease of the electron density. From these results, we conclude that the boundaries of the localized IPAs and EMIC waves were determined by the overlap region of energetic proton enhancement and the plasmasphere. This overlap of ring-current protons and plasmasphere is a favorable condition for the pitch-angle scattering of protons by the EMIC waves. Characteristic magnetic and electric field variations with the IPAs were not observed by the satellite, indicating that the IPAs were not accompanied by field-aligned currents comparable to that of oval auroral arcs.

DOI： 10.1029/2022JA030455

Statistical Study of Subauroral Arc Detachment at Athabasca, Canada: New Insights on STEVE 査読有り

Yadav Sneha, Shiokawa Kazuo, Otsuka Yuichi, Connors Martin

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 127 巻 ( 9 ) 2022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

We present the first comparative statistical study of subauroral arc detachment from the main auroral oval at Athabasca (magnetic latitude = 61.5°N), Canada, for three different types of subauroral arcs: pure red arc, red arc with simultaneous emission in green-line (red + green arc), and STEVE (strong thermal emission velocity enhancement). Based on 15-years (2006–2020) of all-sky imaging observations, this study not only uncovers the occurrence characteristics of different arcs but also provides important insights into the specific geomagnetic conditions under which STEVE develops. Red arc was the most common subauroral arc (139 events), followed by red + green arc (42 events), and STEVE (26 events) was a rare phenomenon. The detachment rate of red and red + green arcs exhibits dependence on both the solar flux and geomagnetic activity. The detachment rate of STEVE was higher during premidnight, whereas that of red and red + green arcs was higher around the midnight sector. The geomagnetic activity was relatively higher for STEVE, the decrease in the AL index and local X-component magnetic variations being ∼2–3 times higher for STEVE as compared to other arcs. STEVE shows a strong association with asymmetric ring current in terms of prominent bay-like enhancement in ASY-H index prior to its detachment. Such bay-like enhancement was ∼4 times higher for STEVE as compared to other arcs. STEVE events were accompanied by dispersionless injection for both electron and proton flux at geosynchronous orbit. These results unambiguously suggest that STEVE develops after substorm associated energy injection and significant intensification of the asymmetric ring current.

DOI： 10.1029/2021JA029856

Quantifying the Size and Duration of a Microburst-Producing Chorus Region on 5 December 2017 査読有り

Elliott S. S., Breneman A. W., Colpitts C., Pettit J. M., Cattell C. A., Halford A. J., Shumko M., Sample J., Johnson A. T., Miyoshi Y., Kasahara Y., Cully C. M., Nakamura S., Mitani T., Hori T., Shinohara I., Shiokawa K., Matsuda S., Connors M., Ozaki M., Manninen J.

GEOPHYSICAL RESEARCH LETTERS 49 巻 ( 15 ) 頁： e2022GL099655 2022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：Geophysical Research Letters

Microbursts are impulsive (<1 s) injections of electrons into the atmosphere, thought to be caused by nonlinear scattering by chorus waves. Although attempts have been made to quantify their contribution to outer belt electron loss, the uncertainty in the overall size and duration of the microburst region is typically large, so that their contribution to outer belt loss is uncertain. We combine datasets that measure chorus waves (Van Allen Probes [RBSP], Arase, ground-based VLF stations) and microburst (>30 keV) precipitation (FIREBIRD II and AC6 CubeSats, POES) to determine the size of the microburst-producing chorus source region beginning on 5 December 2017. We estimate that the long-lasting (∼30 hr) microburst-producing chorus region extends from 4 to 8 (Formula presented.) MLT and 2–5 (Formula presented.) L. We conclude that microbursts likely represent a major loss source of outer radiation belt electrons for this event.

DOI： 10.1029/2022GL099655

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022GL099655

A Story of Developing the Idea of Plasma-Sheet Flow Braking 査読有り

Shiokawa Kazuo

FRONTIERS IN ASTRONOMY AND SPACE SCIENCES 9 巻 2022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：Frontiers in Astronomy and Space Sciences

This paper reports a story of developing the idea of Earthward ion flow braking in the near-Earth plasma sheet and its relationship with substorm onset processes. This idea and the data that support it are the basis for today’s two competing models for substorms: the near-Earth neutral-line model and the current disruption model. The idea was developed when the author was staying at the Max Planck Institute for Extraterrestrial Physics (MPE) from July 1996 to June 1997. The story addresses the colleagues and mentors who had contributed to the development of this idea. The lessons learned from this story are also summarized for students and early-career scientists for their development of new scientific ideas.

DOI： 10.3389/fspas.2022.957776

Collaborative Research Activities of the Arase and Van Allen Probes 査読有り

Miyoshi Y., Shinohara I., Ukhorskiy S., Claudepierre S. G., Mitani T., Takashima T., Hori T., Santolik O., Kolmasova I., Matsuda S., Kasahara Y., Teramoto M., Katoh Y., Hikishima M., Kojima H., Kurita S., Imajo S., Higashio N., Kasahara S., Yokota S., Asamura K., Kazama Y., Wang S. -Y., Jun C. -W., Kasaba Y., Kumamoto A., Tsuchiya F., Shoji M., Nakamura S., Kitahara M., Matsuoka A., Shiokawa K., Seki K., Nose M., Takahashi K., Martinez-Calderon C., Hospodarsky G., Colpitts C., Kletzing Craig, Wygant J., Spence H., Baker D. N., Reeves G. D., Blake J. B., Lanzerotti L.

SPACE SCIENCE REVIEWS 218 巻 ( 5 ) 頁： 38 2022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：Space Science Reviews

This paper presents the highlights of joint observations of the inner magnetosphere by the Arase spacecraft, the Van Allen Probes spacecraft, and ground-based experiments integrated into spacecraft programs. The concurrent operation of the two missions in 2017–2019 facilitated the separation of the spatial and temporal structures of dynamic phenomena occurring in the inner magnetosphere. Because the orbital inclination angle of Arase is larger than that of Van Allen Probes, Arase collected observations at higher L-shells up to L∼ 10. After March 2017, similar variations in plasma and waves were detected by Van Allen Probes and Arase. We describe plasma wave observations at longitudinally separated locations in space and geomagnetically-conjugate locations in space and on the ground. The results of instrument intercalibrations between the two missions are also presented. Arase continued its normal operation after the scientific operation of Van Allen Probes completed in October 2019. The combined Van Allen Probes (2012-2019) and Arase (2017-present) observations will cover a full solar cycle. This will be the first comprehensive long-term observation of the inner magnetosphere and radiation belts.

DOI： 10.1007/s11214-022-00885-4

その他リンク： https://link.springer.com/article/10.1007/s11214-022-00885-4/fulltext.html

Signatures of Auroral Potential Structure Extending Through the Near-Equatorial Inner Magnetosphere 査読有り

Imajo S., Miyoshi Y., Asamura K., Shinohara I., Nose M., Shiokawa K., Kasahara Y., Kasaba Y., Matsuoka A., Kasahara S., Yokota S., Keika K., Hori T., Shoji M., Nakamura S., Teramoto M.

GEOPHYSICAL RESEARCH LETTERS 49 巻 ( 10 ) 2022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：Geophysical Research Letters

The auroral acceleration region plays an important role in the magnetosphere-ionosphere coupling system. In this study, signatures of an auroral U-shaped potential structure were found for the first time in the near-equatorial inner magnetosphere by the Arase satellite at ∼6.0 RE geocentric distance and 11° magnetic latitude. The observed magnetic and electric field variations corresponded to the equatorward motion of the upward field-aligned current and converging perpendicular electric field. Examining the three-dimensional velocity distribution function of H+ and O+ ions, we demonstrate that upflowing ion beams were significantly deflected in an east-west direction with a perpendicular velocity up to ∼80 km/s, which is consistent with the ExB drift velocity. A simple particle drift model with the inferred auroral perpendicular potential presents a new kink-like drift path of ions from the magnetotail, implying that the auroral potential structure has a great impact on particle dynamics in the near-earth plasma sheet.

DOI： 10.1029/2022GL098105

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022GL098105

Slow Contraction of Flash Aurora Induced by an Isolated Chorus Element Ranging From Lower-Band to Upper-Band Frequencies in the Source Region 査読有り

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

GEOPHYSICAL RESEARCH LETTERS 49 巻 ( 9 ) 2022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：Geophysical Research Letters

Flash aurora driven by an isolated chorus element can be a useful ionospheric indicator for identifying the source wave properties via wave-particle interactions. Using ground observation and modeling approaches, here we report the temporal characteristics of flash aurora that depend on the chorus frequency width and the sweep rate. We found that the contraction time increases more than the expansion time in patchy auroral variations, due to the difference in the minimum electron energies resonated with the chorus wave packet away from the equatorial source to higher latitudes. Especially, the contraction time strongly depends on the higher-frequency chorus waves due to cyclotron resonance with lower-energy electrons. The model calculations support that the chorus element ranges from lower-band to upper-band frequencies with respect to half the gyrofrequency at the exact generation region. Our study provides the prompt (milliseconds) chorus-driven electron dynamics through the spatiotemporal characteristics of flash aurora in the ionosphere.

DOI： 10.1029/2021GL097597

Statistical Survey of Arase Satellite Data Sets in Conjunction With the Finnish Riometer Network 査読有り

Thomas Neethal, Kero Antti, Miyoshi Yoshizumi, Shiokawa Kazuo, Hyotyla Miikka, Raita Tero, Kasahara Yoshiya, Shinohara Iku, Matsuda Shoya, Nakamura Satoko, Kasahara Satoshi, Yokota Shoichiro, Keika Kunihiro, Hori Tomoaki, Mitani Takefumi, Takashima Takeshi, Asamura Kazushi, Kazama Yoichi, Wang Shiang-Yu, Jun C-W, Higashio Nana

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 127 巻 ( 5 ) 2022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

During disturbed geomagnetic conditions, the energetic particles in the inner magnetosphere are known to undergo precipitation loss due to interaction with various plasma waves. This study, investigates the energetic particle precipitation events statistically using coordinate observations from the ground riometer network and the inner-magnetospheric satellite mission, Arase. We have compared cosmic noise absorption (CNA) data obtained from the Finnish ground riometer network located in the auroral/sub-auroral latitudes with the comprehensive data set of omnidirectional electron/proton flux and plasma waves in ELF/VLF frequency range from the Arase satellite during the overpass intervals. The study period includes one and a half years of data between March 2017 and September 2018 covering Arase conjunctions with the riometer stations from all magnetic local time sectors. The relation between the plasma flux/waves observed at the satellite with the riometer absorptions are investigated statistically for CNA (absorption >0.5 dB) and non-CNA (absorption <0.5 dB) cases separately. During CNA events, Arase observed elevated electron flux in the medium energy range (2–100 keV), and plasma wave activity in the whistler-mode frequency range (0.5–3 kHz) of the spectra. Our study provides an estimate of the statistical dependence of the electron flux and plasma wave observations at Arase with the ground reality of actual precipitation.

DOI： 10.1029/2022JA030271

Simultaneous Observations of EMIC-Induced Drifting Electron Holes (EDEHs) in the Earth's Radiation Belt by the Arase Satellite, Van Allen Probes, and THEMIS 査読有り

Nakamura S., Miyoshi Y., Shiokawa K., Omura Y., Mitani T., Takashima T., Higashio N., Shinohara I, Hori T., Imajo S., Matsuoka A., Tsuchiya F., Kumamoto A., Kasahara Y., Shoji M., Spence H., Angelopoulos V

GEOPHYSICAL RESEARCH LETTERS 49 巻 ( 5 ) 2022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

We present an observation of rapid flux depressions in relativistic electrons, which is referred to as “EMIC-induced drifting electron holes (EDEHs).” The Arase, Van Allen Probes, and THEMIS detected simultaneously electron flux fluctuations. The time variation of flux shows depressions of 1-min scale with energy dispersion, which appear only in the relativistic energy range and small pitch angles. These characteristics of the flux depression indicate that electromagnetic ion cyclotron waves caused pitch angle scattering on a short time scale in a longitudinally limited region. The Arase satellite detected the local depression of the phase space density of 1,000 MeV/G electron, indicating that EMIC waves cause the true loss of electrons. Tracing the energy dispersion profile of EDEHs, we show that EDEHs are formed at localized region in the dusk side. Multisatellite observations demonstrate that a series of EDEHs eventually cause a substantial depression of the radiation belt on 1-hr time scale.

DOI： 10.1029/2021GL095194

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021GL095194

Detecting Equatorial Plasma Bubbles on All-Sky Imager Images Using Convolutional Neural Network 査読有り

Srisamoodkham W., Shiokawa K., Otsuka Y., Ansari K., Jamjareegulgarn P.

Lecture Notes in Networks and Systems 461 巻頁： 481 - 487 2022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：Lecture Notes in Networks and Systems

This paper proposes initially to apply convolutional neural network (CNN) for detecting the equatorial plasma bubbles on the ASI images. The considered CNN model is the YOLO v3 tiny model under a deep learning API (Keras), running on top of the machine learning platform (TensorFlow). Our program for EPB detection is written in Python that is extended easily to combine into a space weather web site for detecting and notifying EPBs in our next step. The results show that the YOLO v3-based CNN can detect the EPBs in ASI images with different intensities obtained from many countries. The threshold is tested and selected to be 0.40 suitably for detecting the anomaly (EPB existence). The maximum anomalous value is selected to decide the EPB occurrence.

DOI： 10.1007/978-981-19-2130-8_38

Horizontal Inhomogeneity in the D-Region Ionosphere During an X-Class Solar Flare Determined by OCTAVE VLF Observations 査読有り

Masaharu Nakayama, Hiroyo Ohya, Fuminori Tsuchiya, Kenro Nozaki, Kazuo Shiokawa, Hiroyuki Nakata

URSI Radio Science Letters 4 巻 2022年

RESPONSE OF THE D-REGION IONOSPHERE TO FIREBALLS USING VLF/LF TRANSMITTER SIGNALS 査読有り

Suzuki, T; Ohya, H; Tsuchiya, F; Shiokawa, K; Nakata, H

18TH ANNUAL MEETING OF THE ASIA OCEANIA GEOSCIENCES SOCIETY, AOGS 2021 頁： 215 - 217 2022年

Variations of Zonal Wind Velocity in the Thermosphere Observed at Southeast Asian Sector During Quiet and Active Geomagnetic Days 査読有り

Sarudin Idahwati, Hamid Nurul Shayana Abdul, Abdullah Mardina, Rusli Fatin Nur Syakirah Mohd, Otsuka Yuichi, Shiokawa Kazuo, Yatini Clara, Komonjinda Siramas, Somboon Ekkarach

JURNAL FIZIK MALAYSIA 43 巻 ( 1 ) 頁： 10025 - 10035 2022年

Spatio-Temporal Distributions of Lightning Stroke Charge Using ELF and Meteorological Data 査読有り

Hobara Y., Ohashi T., Shiraishi T., Shiokawa K.

Lecture Notes in Electrical Engineering 842 巻頁： 329 - 337 2022年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：Lecture Notes in Electrical Engineering

In this paper lightning stroke charges are estimated remotely by using combinations of Extremely Low Frequency (ELF) radio waves, conventional Lightning Locating System (LLS) and local meteorological information for the first time. Each lightning stroke location from LLS and corresponding transient signature of ELF magnetic field observed at a long distance (−1000 km between lightning stroke and observation site) are utilized to estimate the charge moment change (CMC) of the lightning stroke. The lightning stroke charge Q is then derived by dividing the CMC by the altitude of the neutralized lightning charge. The corresponding altitude of the neutralized lightning charge for each stroke is determined by assuming local −20 °C altitude for a positive stroke (−10 °C altitude for a negative strokes) from MesoScale Model (MSM). Spatial and temporal frequency distributions of energetic lightning (large amount of stroke charge) and cumulative frequency distributions of stroke charge in northwestern part of Japan in local summer and winter seasons for 4 years were derived. The spatial occurrence frequency distributions indicate that lightning strokes with a large amount of neutralized charge occur more frequently in inland areas during summertime and in coastal areas in winter. The cumulative frequency distribution indicates that positive polarity lightning strokes in winter tend to have a large charge. Our statistical results are in good agreement with the lightning properties inferred from local observations, and are considered to be useful information not only to study electrical properties of thunderstorms but also for future maintenance planning of power grid systems in wide areas and mitigation of lightning damages.

DOI： 10.1007/978-981-16-8690-0_30

Spatio-Temporal Characteristics of Energetic Lightning in Southeast Asia: Preliminary Statistical Results 査読有り

Shunsuke Akama, Yasuhide Hobara, Amir Izzani Mohamed, Chandima Gomes, Kazuo Shiokawa, Shu Hirai, Hiroshi Kikuchi, Michael Stock

Lecture Notes in Electrical Engineering 842 巻頁： 317 - 327 2022年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

The region of Southeast Asia is known as one of the lightning-prone areas in the world. However, spatial and temporal distributions of high-energy lightning discharges, which cause natural disasters e.g. significant damages to local power grid systems and forest fires, are still unknown. This paper reports initial results on the statistical characteristics of energetic lightning around Malay Peninsula. Highly accurate timing and location as well as lightning peak current (Ip ) of lightning strokes were obtained by ENTLN (Earth Networks Total Lightning Network), while the vertical charge moment change Qds as a proxy of high-energy lightning was derived by using ground-based ELF magnetic field observations in Pahang, Malaysia with a small threshold of less than 10 C·km. The characteristics of energetic lightning for both rainy and dry seasons were successfully derived for the first time in this region. The results indicate that highly energetic lightning occur frequently throughout the rainy and dry seasons, mainly over the Malacca Strait. Long-term statistical analysis with an extended data analysis period is necessary to understand further the seasonal and yearly dependences of energetic lightning and their relations with local climate conditions.

DOI： 10.1007/978-981-16-8690-0_29

Predictability of variable solar-terrestrial coupling 査読有り

Daglis Ioannis A., Chang Loren C., Dasso Sergio, Gopalswamy Nat, Khabarova Olga V, Kilpua Emilia, Lopez Ramon, Marsh Daniel, Matthes Katja, Nandy Dibyendu, Seppala Annika, Shiokawa Kazuo, Thieblemont Remi, Zong Qiugang

ANNALES GEOPHYSICAE 39 巻 ( 6 ) 頁： 1013 - 1035 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：Annales Geophysicae

In October 2017, the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP) Bureau established a committee for the design of SCOSTEP's Next Scientific Programme (NSP). The NSP committee members and authors of this paper decided from the very beginning of their deliberations that the predictability of the Sun-Earth System from a few hours to centuries is a timely scientific topic, combining the interests of different topical communities in a relevant way. Accordingly, the NSP was christened PRESTO -PREdictability of the variable Solar-Terrestrial cOupling. This paper presents a detailed account of PRESTO; we show the key milestones of the PRESTO roadmap for the next 5 years, review the current state of the art and discuss future studies required for the most effective development of solar-terrestrial physics.

DOI： 10.5194/angeo-39-1013-2021

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