掲載種別：研究論文（学術雑誌）   出版者・発行元：Annals of Geophysics  

Fluctuations in Solar Wind (SW) and Interplanetary Magnetic Field (IMF) have a relevant effect on the Geomagnetic Field (GF) measurements particularly during extreme space weather events. The current study investigates the variations of horizontal (H), vertical (Z) geomagnetic components under quiet and disturbed IMF and solar conditions as well as the effect of underground conductivity on the stationary geomagnetic measurements in Japan. Results of data analysis show that the response of the GF to IMF and solar parameters fluctuations is variable. The H and Z components were in good agreement with high visual correlation along a latitudinal profile across Japan during quiet times. On the other hand, during the disturbed times related to a Coronal Mass Ejection (CME) launched on 13 May 2005, the GF components varied with the disturbance of IMF and solar parameters. The H components showed highly correlated variations with a significant reduction along the examined profile due to the intensified ionospheric currents, while the Z components recorded in the northern part of Japan showed abnormal daily variations pattern (positive daily variations) with an enhanced amplitude which is opposite to the normal behavior of daily variations recorded in the central and southern parts of Japan (negative daily variations). The observed enhanced and abnormal daily variation of Z components in north Japan, which we consider a remarkable observation here, is possibly linked with underground conductivity anomaly in this region.

DOI： 10.4401/ag-9021

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Advances in Space Research  

This study introduced a simplified, integrated computational model to estimate the drag coefficient and surface charging within the plasma wake of Low Earth Orbit (LEO) spacecraft influenced by various solar activities. The model constituted four core modules: a solver for the solar wind-magnetosphere interaction, a magnetosphere-ionosphere coupling for electric field mapping, an ionization model for the F-layer of the ionosphere, and an estimation model for excess satellite drag and plasma wake size. The initial module adopted a simplified 1D ideal Magnetohydrodynamic (MHD) model while incorporating magnetosphere-ionosphere interactions to derive electric field data near Earth's boundary. A simplified ionospheric model for the F-layer was implemented to compute the O+ and electron densities. Subsequently, the spacecraft drag coefficient and the plasma wake size were determined for varying solar wind speed inputs corresponding to quiet, intense, and extreme space weather conditions. In the case of extreme conditions with a solar wind speed of 1000 km/s, the results indicated that the excess satellite drag coefficient and plasma wake size increased to around ten percent.

DOI： 10.1016/j.asr.2023.12.064

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担当区分：筆頭著者,　責任著者  

DOI： 10.5194/egusphere-egu24-1630

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担当区分：筆頭著者,　責任著者  

DOI： 10.22541/au.170328011.17032719/v1

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Space Weather  

Abstract

During a few solar energetic particle (SEP) events, solar protons were trapped within the geomagnetic field and reached the outer edge of the inner radiation belt. We reproduced this phenomenon by modeling the proton flux distribution at the Low‐Earth Orbit (LEO) for different geomagnetic conditions during solar particle events. We developed a three‐dimensional relativistic test particle simulation code to compute the 70–180 MeV solar proton Lorentz trajectories in low L‐shell range from 1 to 3. The Tsyganenko model (T01) generated the background static magnetic field with the IGRF (v12) model. We have selected three Dst index values: −7, −150, and −210 nT, to define quiet time, strong, and severe geomagnetic storms and to generate the corresponding inner magnetic field configurations. Our results showed that the simulated solar proton flux was more enhanced in the high‐latitude regions and more expanded toward the lower latitude range as long as the geomagnetic storm was intensified. Satellite observations and geomagnetic cutoff rigidities confirmed the numerical results. Furthermore, the LEO proton flux distribution was deformed, so the structure of the proton flux inside the South Atlantic Anomaly (SAA) became longitudinally extended as the Dst index decreased. Moreover, we have assessed the corresponding radiation environment of the LEO mission. We realized that, for a higher inclined LEO mission during an intense geomagnetic storm (Dst = −210 nT), the probability of the occurrence of the Single Event Upset (SEU) rates increased by 19% and the estimated accumulated absorbed radiation doses increased by 17% in comparison with quiet conditions.

DOI： 10.1029/2023sw003664

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Journal of Radio Frequency Identification  

We have studied the radiation environment of LEO spacecraft when passing through the South Atlantic Anomaly (SAA) during the geomagnetic storm event of 15 May 2005. The 70-180 MeV proton flux information were numerically obtained from a simulation model of the inner radiation belt. The radiation analysis was consisted of two parts: the estimation of the Single Event Upset (SEU) rates and the absorbed radiation doses. One of the characteristics of the SAA at 800 km altitude during the recovery phase of the geomagnetic storm was the enhancement of its southern proton flux cell. It was found that the excess SEU rates and absorbed radiation doses could reach at least 200 % and 70 % respectively during the recovery phase in comparison to the initial phase of the geomagnetic storm. The estimated radiation results were in a good agreement with observations.

DOI： 10.1109/JRFID.2022.3163441

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記述言語：その他   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  

In order to estimate the proton flux variations occurring in the South Atlantic Anomaly (SAA) caused by the geodipole tilting angle and the Dst index variations, we performed three dimensional relativistic test particle simulations to calculate the trajectories of high-energy protons (70–180 MeV), where the static background magnetic field was calculated by the Tsyganenko models T01/TS05 combined with IGRF-12. As various parameters characterize the SAA proton flux, the study considered the maximum proton flux and the area of the SAA. Among many different parameters that define the space weather conditions, we considered the geodipole tilting angle and the Dst index. The numerical results showed that (1) the proton flux intensity was increased in the SAA for small geodipole tilting angles, which was confirmed by observations, and that (2) the proton flux intensity was also increased for significantly low Dst index.

DOI： 10.1016/j.jastp.2021.105808

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記述言語：その他   掲載種別：研究論文（その他学術会議資料等）   出版者・発行元：2021 IEEE International Conference on Wireless for Space and Extreme Environments, WiSEE 2021  

In this study, we assessed the Single Event Upset (SEU) rates of a LEO mission due to its passage in the South Atlantic Anomaly (SAA) during a geomagnetic storm. The South Atlantic Anomaly (SAA) represents a dangerous source of radiation for the LEO operations. Since the space weather continuously affects the inner magnetosphere condition, therefore, the inner radiation belt is subjected to significant variations, in particular during extreme space weather conditions. As the radiation environment depends essentially on the particle flux information, we have developed a numerical model to simulate the inner proton belt dynamics. In our previous work [Girgis et al. (2020b)], the short-Term variations of the inner proton belt was investigated according to the geomagnetic storm event of 15 May 2005 and the kinetic energy range for the implemented protons was from 70 to 180 MeV. The objective of this paper is to extend the previous work by assessing the corresponding SEU rates of the RAM devices mounted in a spacecraft operating in a circular orbit of 850 km, given the proton flux map information as the output results of the inner proton belt numerical model. It was concluded from the inner proton belt simulations during the geomagnetic storm, that the SAA proton flux was significantly enhanced, by > 10 % after the beginning of the storm and during the recovery storm phase. Consequently, the SEU rates were increased by 40 % during the recovery phase of the geomagnetic storm. The earlier and more accurate prediction of the SEU rates can save a LEO satellite mission from unexpected proton-induced single event upset rates during extreme space weather conditions such as geomagnetic storms.

DOI： 10.1109/wisee50203.2021.9613828

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記述言語：その他   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  

A test particle simulation code was developed to simulate the inner proton belt response during the intense geomagnetic storm of 15 May 2005. The guiding center model was implemented to compute the proton trajectories with an energy range of 70–180 MeV. The time-varying magnetic field model implemented in the simulations was computed by the Tsyganenko model TS05 with the associated inductive electric field. One of the most important features of the low-earth orbit (LEO) environment is the South Atlantic Anomaly, which imposes a dangerous radiation load on most LEO missions. This research aims to investigate the proton flux variations in the anomaly region with respect to space weather conditions. The results showed that during the main phase of the geomagnetic storm, the proton flux in the SAA decreased, whereas, throughout the initial and recovery phases, the proton flux was increased at most of the altitudes. Satellite measurements confirmed numerical results.

添付ファイル： swsc210016.pdf

DOI： 10.1051/swsc/2021031

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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  

We studied the space weather effects on the South Atlantic Anomaly (SAA) magnetic response using Tsyganenko models. For the physical parameters characterizing the SAA, the study considered the minimum magnetic field, the location (longitude and latitude) of the SAA center, and the area of the SAA. Regarding the space weather parameters, we considered the solar wind dynamic pressure, the interplanetary magnetic field components, ByIMF and BzIMF, the Dst index, and the geodipole tilting angle. To study the magnetic field response of the SAA, several different versions of the Tsyganenko models, namely, T96, T01, and TS05, were used to describe the external magnetic field contributions. The main internal magnetic field was calculated by the International Geomagnetic Reference Field (IGRF-12). The magnetic field study of the SAA was realized in long- and short-term (seasonal and diurnal) variations. We found that the Dst index and the geodipole tilting angle were the strongest influencing parameters on the SAA magnetic field response at all altitudes. Moreover, it was revealed that both magnetic poles might be a possible cause of the SAA magnetic field response, resulting from the space weather conditions. Furthermore, the magnetic field behavior of the SAA was affected by hourly variations, where the largest changes occurred at dayside.[Figure not available: see fulltext.].

添付ファイル： 0615KG_publication1.pdf

DOI： 10.1186/s40623-020-01221-2

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その他リンク： http://link.springer.com/article/10.1186/s40623-020-01221-2/fulltext.html

記述言語：英語   掲載種別：研究論文（研究会，シンポジウム資料等）   出版者・発行元：Copernicus GmbH  

<p>In this study, we assess the hourly variations of the three-dimensional proton flux distribution inside the South Atlantic Anomaly (SAA) during a geomagnetic storm. We have developed a relativistic three-dimensional guiding center test particle simulation code in order to compute the proton trajectories in a time-varying magnetic field background provided by Tsyganenko model TS05 and the corresponding time-varying inductive electric field. The Dst index is the main input parameter to the simulation model, while the maximum proton flux, the area of the SAA calculated below a selected threshold, and the penetration depth of the protons are the main output variables investigated in this study were. Since the LEO spacecraft and human-related activities are already affected by space weather conditions, the South Atlantic Anomaly (SAA) is also believed to create an additional source of risk. As the radiation environment depends essentially on the particle flux, the objective of this study is to estimate quantitatively the proton flux variations inside the South Atlantic Anomaly (SAA) in quiet and in storm conditions. So far, it was found that after several drift periods, the protons in the South Atlantic Anomaly (SAA) could penetrate to lower altitudes during geomagnetic storm event, and that, the SAA maximum flux value and the corresponding area, varied differently with respect to altitudes. Numerical results were compared with observations by NOAA 17 and RD3R2 instrument mounted on International Space Station (ISS).</p>

添付ファイル： egu.pdf

DOI： 10.5194/egusphere-egu2020-1551

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担当区分：筆頭著者,　責任著者   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）  

添付ファイル： 0615KG_publication3.pdf

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開催年月日： 2024年4月

記述言語：英語   会議種別：ポスター発表  

開催地：ウィーン   国名：オーストリア共和国  

DOI： https://doi.org/10.5194/egusphere-egu24-1630

その他リンク： https://meetingorganizer.copernicus.org/EGU24/EGU24-1630.html

開催年月日： 2024年2月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：九州大学西新プラザ   国名：日本国  

開催年月日： 2024年2月

記述言語：英語   会議種別：ポスター発表  

開催地：国際連合ウィーン事務局   国名：オーストリア共和国  

開催年月日： 2023年12月

記述言語：英語   会議種別：シンポジウム・ワークショップ パネル（指名）  

開催地：兵庫県神戸市   国名：日本国  

開催年月日： 2023年11月

記述言語：英語   会議種別：ポスター発表  

開催地：名古屋市国際展示場   国名：日本国  

その他リンク： https://www.aappsdpp.org/DPP2023/html/3contents/pdf/5473.pdf

開催年月日： 2024年11月

記述言語：英語   会議種別：シンポジウム・ワークショップ パネル（公募）  

開催地：京都府京都市   国名：日本国  

開催年月日： 2023年9月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：宮城県仙台市   国名：日本国  

その他リンク： https://www.sgepss.org/meeting/archive/154/html/program/pdf/R010/R010-23.pdf

開催年月日： 2023年6月

記述言語：日本語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

開催地：九州大学　伊都キャンパス   国名：日本国  

開催年月日： 2023年5月

記述言語：英語   会議種別：ポスター発表  

開催地：幕張メッセ、千葉県   国名：日本国  

開催年月日： 2022年5月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：相模原市立産業会館 相模原市   国名：日本国  

その他リンク： https://www.sgepss.org/meeting/archive/152/html/program/pdf/R010/R010-20.pdf

開催年月日： 2022年10月

記述言語：英語   会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

開催地：九州大学　筑紫キャンパス   国名：日本国  

開催年月日： 2022年10月

記述言語：英語   会議種別：口頭発表（一般）  

開催地：オンライン  

その他リンク： https://www.aappsdpp.org/DPP2022/html/3contents/pdf/topical/5383.pdf