宇宙ー地球連結シミュレーションを軸とした放射線帯変動メカニズムの実証的研究

• Project/Area Number: 23K20241
• Project/Area Number (Other): 20H01960 (2020-2023)
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Multi-year Fund (2024); Single-year Grants (2020-2023)
• Section: 一般
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Kyoto University
• Principal Investigator: 海老原 祐輔 京都大学, 生存圏研究所, 教授 (80342616)
• Co-Investigator(Kenkyū-buntansha): 田中 高史 九州大学, 国際宇宙惑星環境研究センター, 博士研究員 (70346766)
• Project Period (FY): 2020-04-01 – 2025-03-31
• Project Status: Declined (Fiscal Year 2024)
• Budget Amount: ¥17,550,000 (Direct Cost: ¥13,500,000、Indirect Cost: ¥4,050,000); Fiscal Year 2024: ¥2,860,000 (Direct Cost: ¥2,200,000、Indirect Cost: ¥660,000); Fiscal Year 2023: ¥2,730,000 (Direct Cost: ¥2,100,000、Indirect Cost: ¥630,000); Fiscal Year 2022: ¥2,730,000 (Direct Cost: ¥2,100,000、Indirect Cost: ¥630,000); Fiscal Year 2021: ¥4,030,000 (Direct Cost: ¥3,100,000、Indirect Cost: ¥930,000); Fiscal Year 2020: ¥5,200,000 (Direct Cost: ¥4,000,000、Indirect Cost: ¥1,200,000)
• Keywords: 磁気圏 / 太陽風ー地球相互作用 / 放射線帯 / シミュレーション / 地球磁気圏 / 電磁流体シミュレーション / 地球放射線帯 / 太陽風ー磁気圏ー電離圏ー地球結合

Outline of Research at the Start

地球近くの宇宙空間では相対論的な速さを持つ粒子が地球磁場に捕捉され、放射線帯を形成している。放射線帯は地磁気擾乱に応じて増加する場合と減少する場合があり、その変動は長年の謎となっている。電磁波動の成長が放射線帯の変動を決定している公算が大きいが、これらの粒子群が惑星間空間からエネルギーを獲得するまでの過程はよく分かっていない。本研究では、最新のシミュレーション、最新の電磁波動成長理論、史上最密の観測データを組み合わせ、惑星間空間から地球本体そして放射線帯に至るエネルギーの流れの全貌と、放射線帯変動に至るまでの諸過程の役割とその寄与分を定量的に明らかにする。

Outline of Annual Research Achievements

放射線帯形成理論として有力視されている内部加速説は、主に磁気圏対流によって内部磁気圏に運ばれた低エネルギー電子がエネルギー源となって電磁波動が成長し、その波が電子を加速するという考え方である。磁気圏対流は内部加速説の前提で、欠かせない要素であるが、その発生機構はよく分かっていない。磁気流体シミュレーションを用い、磁気再結合したばかりの地球の磁力線を太陽風プラズマが引っ張り、磁気圏起源のプラズマを巻き込みつつ、領域１型沿磁力線電流が生成されていることを前年度に明らかにしたが、さらに領域１型沿磁力線電流の周囲を磁場エネルギー（ポインティング・フラックス）が螺旋状に取り囲んでいることが明らかになり、領域１型沿磁力線電流、地球近傍の磁気圏対流、太陽風から極域電離圏に至るエネルギーの輸送の３者が一体となっている可能性が示された。L=1.3という深内部磁気圏に輸送される電子とその特徴的なエネルギースペクトル（ゼブラ構造）を再現することに成功した。沿磁力線電流の大きさとよい対応があり、その影響が深内部磁気圏に及んでいることを実証した。
内部加速説のもう一つの柱はコーラス波と呼ばれる電磁波動の励起とそれによる電子のMeV帯への加速である。コーラス波の成長とその後生成される強いサブパケットの形成を決める上で、コーラス波の生成領域の移動速度が重要であることを示した。また、低周波帯域コーラス波が斜め伝搬する場合、電子を効率よく散乱することを示した。
放射線帯電子を散乱する原因として、電磁イオンサイクロトロン波（EMIC波）によるピッチ角散乱が有力視されている。EMIC波を励起するのはkeV帯のイオンで、その直接の起源は磁気圏尾部にあると考えられている。磁気流体シミュレーションで得られた電場・磁場のなかでH+とO+の軌道計算を行い、サブストーム時に内部磁気圏外縁部で急増するイオンを再現した。

Research Progress Status

令和5年度が最終年度であるため、記入しない。

Strategy for Future Research Activity

令和5年度が最終年度であるため、記入しない。

Research Products

• [Journal Article] Upstream motion of chorus wave generation: comparisons with observations (2024)
  • Author(s): Foster John C.、Erickson Philip J.、Omura Yoshiharu
  • Journal Title: Frontiers in Astronomy and Space Sciences Volume: 11
  • DOI: 10.3389/fspas.2024.1374331
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Possible Global Generation Region of Nonlinear Whistler‐Mode Chorus Emission Waves at Mercury (2024)
  • Author(s): Ozaki Mitsunori、Kondo Takeru、Yagitani Satoshi、Hikishima Mitsuru、Omura Yoshiharu
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 129 Issue: 2
  • DOI: 10.1029/2023ja032086
  • Peer Reviewed
• [Journal Article] Generation mechanism of Region 1 field-aligned current and energy transfer from solar wind to polar ionosphere (2024)
  • Author(s): Yusuke Ebihara、Takashi Tanaka
  • Journal Title: REVIEWS OF MODERN PLASMA PHYSICS Volume: 印刷中 Issue: 1
  • DOI: 10.1007/s41614-024-00154-7
  • Peer Reviewed / Open Access
• [Journal Article] Intensification of the Electron Zebra Stripes in the Earth's Inner Magnetosphere During Geomagnetic Storms (2024)
  • Author(s): Pandya Megha、Ebihara Yusuke、Tanaka Takashi、Manweiler Jerry W.、Vines Sarah K.
  • Journal Title: Geophysical Research Letters Volume: 51 Issue: 3
  • DOI: 10.1029/2023gl107822
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Precipitation Rates of Electrons Interacting With Lower‐Band Chorus Emissions in the Inner Magnetosphere (2023)
  • Author(s): Hsieh Yi‐Kai、Omura Yoshiharu
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 128 Issue: 6
  • DOI: 10.1029/2023ja031307
  • Peer Reviewed / Open Access
• [Journal Article] Nighttime Geomagnetic Response to Jumps of Solar Wind Dynamic Pressure: A Possible Cause of Qu?bec Blackout in March 1989 (2023)
  • Author(s): Zhang T.、Ebihara Y.、Tanaka T.
  • Journal Title: Space Weather Volume: 21 Issue: 11
  • DOI: 10.1029/2023sw003493
  • Peer Reviewed / Open Access
• [Journal Article] Radial transport of Io plasma from the inner magnetosphere to the tail (2023)
  • Author(s): Tanaka, T., Ebihara, Y., Watanabe, M., Fujita, S., & Kataoka, R.
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 128 Issue: 5
  • DOI: 10.1029/2022ja030891
  • Peer Reviewed
• [Journal Article] Formation of Electron Zebra Stripes Observed on 8 September 2017 (2023)
  • Author(s): Pandya Megha、Ebihara Yusuke、Tanaka Takashi、Manweiler Jerry W.
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 128 Issue: 4
  • DOI: 10.1029/2022ja030950
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Generation of Field‐Aligned Currents During Substorm Expansion: An Update (2023)
  • Author(s): Ebihara Yusuke、Tanaka Takashi
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 128 Issue: 2 Pages: 1-17
  • DOI: 10.1029/2022ja031011
  • Peer Reviewed / Open Access
• [Journal Article] L‐Value and Energy Dependence of 0.1-50 keV O+, He+, and H+ Ions for CME and CIR Storms Over the Entire Van Allen Probes Era (2022)
  • Author(s): Pandya Megha、Bhaskara Veenadhari、Ebihara Yusuke、Reeves G. D.
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 127 Issue: 9
  • DOI: 10.1029/2022ja030568
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Unified theory of the arc auroras: Formation mechanism of the arc auroras conforming general principles of convection and FAC generation (2022)
  • Author(s): Tanaka, T., Watanabe, M., Ebihara, Y., Fujita, S., Nishitani, N., & Kataoka, R.
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 127 Issue: 9
  • DOI: 10.1029/2022ja030403
  • Peer Reviewed
• [Journal Article] Poleward Moving Auroral Arcs and Pc5 Oscillations (2022)
  • Author(s): Sakurai T.、Wright A. N.、Takahashi K.、Elsden T.、Ebihara Y.、Sato N.、Kadokura A.、Tanaka Y.、Hori T.
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 127 Issue: 8
  • DOI: 10.1029/2022ja030362
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Instantaneous Achievement of the Hall and Pedersen-Cowling Current Circuits in Northern and Southern Hemispheres During the Geomagnetic Sudden Commencement on 12 May 2021 (2022)
  • Author(s): Kikuchi Takashi、Araki Tohru、Hashimoto Kumiko K.、Ebihara Yusuke、Tanaka Takashi、Nishimura Yukitoshi、Vichare Geeta、Sinha Ashwini K.、Chum Jaroslav、Hosokawa Keisuke、Tomizawa Ichiro、Tanaka Yoshimasa、Kadokura Akira
  • Journal Title: Frontiers in Astronomy and Space Sciences Volume: 9 Pages: 879314-879314
  • DOI: 10.3389/fspas.2022.879314
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Where Is Region 1 Field‐Aligned Current Generated? (2022)
  • Author(s): Ebihara Yusuke、Tanaka Takashi
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 127 Issue: 3
  • DOI: 10.1029/2021ja029991
  • Peer Reviewed
• [Journal Article] Roles of the M-I coupling and plasma sheet dissipation on the growth-phase thinning and subsequent transition to the onset (2021)
  • Author(s): Tanaka, T., Ebihara, Y., Watanabe, M., Den, M., Fujita, S., Kikuchi, T., Hashimoto, K. K., Nishitani, N., & Kataoka, R.
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 126 Issue: 12
  • DOI: 10.1029/2021ja029925
  • Peer Reviewed
• [Journal Article] Development of the substorm as a manifestation of convection transient (2021)
  • Author(s): Tanaka, T., Ebihara, Y., Watanabe, M., Den, M., Fujita, S., Kikuchi, T., Hashimoto, K. K., & Kataoka, R.
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 126 Issue: 10
  • DOI: 10.1029/2020ja028942
  • Peer Reviewed
• [Journal Article] Three‐Dimensional Closure of Field‐Aligned Currents in the Polar Ionosphere (2021)
  • Author(s): Yano Yuto、Ebihara Yusuke
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 126 Issue: 9
  • DOI: 10.1029/2021ja029421
  • NAID: 120007187503
  • Peer Reviewed
• [Journal Article] Global simulation of the Jovian magnetosphere: Transitional structure from the Io plasma disk to the plasma sheet (2021)
  • Author(s): Tanaka, T., Ebihara, Y., Watanabe, M., Fujita, S., & Kataoka, R.
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 126 Issue: 6
  • DOI: 10.1029/2021ja029232
  • Peer Reviewed
• [Journal Article] Formation and release of the Harang reversal relating with the substorm onset process (2021)
  • Author(s): Tanaka, T., Ebihara, Y., Watanabe, M., Den, M., Fujita, S., Kikuchi, T., Hashimoto, K. K. , and Kataoka, R.
  • Journal Title: Journal of Geophysical Research: Space Physics Volume: 126 Issue: 1
  • DOI: 10.1029/2020ja028170
  • Peer Reviewed
• [Presentation] サブストーム・オンセット時に急増する沿磁力線電流の生成 (2023)
  • Author(s): Yusuke Ebihara; Takashi Tanaka
  • Organizer: Japan Geoscience Union (JpGU) Meeting 2023
  • Int'l Joint Research
• [Presentation] 沿磁力線電流ダイナモと地磁気サブストーム発達の関係について (2023)
  • Author(s): 海老原祐輔; 田中高史
  • Organizer: 地球電磁気・地球惑星圏学会 2023年秋季年会（第154回講演会・総会）
• [Presentation] Generation of field-aligned currents during substorm expansion: The latest updates (2023)
  • Author(s): Yusuke Ebihara; Takashi Tanaka
  • Organizer: The 15th international conference on substorms (ICS-15)
  • Int'l Joint Research / Invited
• [Presentation] サブストーム時の地球近傍 プラズマシートにおけるイオンの 加速率のエネルギー、ピッチ角、 質量、電荷依存性 (2023)
  • Author(s): 水野 雄太, 海老原 祐輔, 田中 高史
  • Organizer: 地球電磁気・地球惑星圏学会 2023年秋季年会（第154回講演会・総会）
• [Presentation] Generation mechanism of Region 1 field-aligned current (2022)
  • Author(s): Ebihara, Y.
  • Organizer: Association of Asia Pacific Physical Societies-Division of Plasma Physics (AAPPS-DPP)
  • Int'l Joint Research / Invited
• [Presentation] Mutual coupling between magnetosphere and low-latitude ionosphere during magnetic storms and substorms (2022)
  • Author(s): Ebihara, Y.
  • Organizer: 16th International Symposium on Equatorial Aeronomy (ISEA)
  • Int'l Joint Research / Invited
• [Presentation] Geomagnetically induced current (GIC) at low latitudes: Major characteristics and prediction for extreme events (2022)
  • Author(s): Ebihara, Y.
  • Organizer: 16th International Symposium on Equatorial Aeronomy (ISEA)
  • Int'l Joint Research / Invited
• [Presentation] Generation mechanism of Region 1 field-aligned current (2022)
  • Author(s): Ebihara, Y.
  • Organizer: The 15th Asia-Pacific Physics Conference
  • Int'l Joint Research / Invited
• [Presentation] Magnetosphere-ionosphere coupling and consequent disturbances: A tribute to Dr. Yohsuke Kamide (2022)
  • Author(s): Ebihara, Y.
  • Organizer: Asia Oceania Geosciences Society (AOGS)
  • Int'l Joint Research / Invited
• [Presentation] Generation region of Region 1 field-aligned current (2022)
  • Author(s): Ebihara, Y., and Tanaka, T.
  • Organizer: Japan Geoscience Union (JpGU) Meeting 2022
  • Int'l Joint Research
• [Presentation] Generation of the Electron Zebra Stripes in the Earth's Inner Magnetosphere (2022)
  • Author(s): Pandya, M., Y. Ebihara and T. Tanaka
  • Organizer: 地球電磁気・地球惑星圏学会
• [Presentation] Region1field-alignedcurrentandenergytransferfromsolarwindtopolarionosphere (2022)
  • Author(s): 海老原祐輔, 田中高史
  • Organizer: 地球電磁気・地球惑星圏学会
• [Presentation] MHDsimulationsofresponsesofionosphericcurrentsandgroundelectricfield variationsunderdifferentsolarwindconditions (2022)
  • Author(s): 張天, 海老原祐輔, 田中高史
  • Organizer: 地球電磁気・地球惑星圏学会
• [Presentation] オーロラ爆発を駆動する太陽風ー地球間エネルギー移送・変換過程 (2022)
  • Author(s): 海老原祐輔, 田中高史
  • Organizer: 日本物理学会第77回年次大会
  • Invited
• [Presentation] How do auroral substorms depend on Earth's dipole magnetic moment? (2021)
  • Author(s): Ebihara, Y., and T. Tanaka
  • Organizer: Japan Geoscience Union (JpGU) Meeting 2021
  • Int'l Joint Research
• [Presentation] Role of magnetosphere-ionosphere coupling in evolution of auroral substorm as viewed from global MHD simulation (2021)
  • Author(s): Ebihara, Y., and T. Tanaka,
  • Organizer: Joint Scientific Assembly IAGA-IASPEI 2021
  • Int'l Joint Research / Invited
• [Presentation] Region 1沿磁力線電流の生成領域 (2021)
  • Author(s): 海老原祐輔, 田中高史,
  • Organizer: 地球電磁気・地球惑星圏学会2021年秋学会
• [Presentation] 沿磁力線電流と電離圏電流の3次元結合 (2021)
  • Author(s): 矢野 有人, 海老原 祐輔
  • Organizer: 地球電磁気・地球惑星圏学会2021年秋学会
• [Presentation] 3-dimensional coupling between field-aligned currents and ionospheric currents (2021)
  • Author(s): Y. Yano and Y. Ebihara
  • Organizer: American Geophysical Union
  • Int'l Joint Research
• [Presentation] A journey of energy from solar wind to polar ionosphere as viewed from global MHD simulation (2020)
  • Author(s): Ebihara, Y., and T. Tanaka
  • Organizer: Japan Geoscience Union (JpGU)- (American Geophysical Union) AGU Joint Meeting 2020
  • Int'l Joint Research / Invited
• [Presentation] Where is nonlinear growth of whistler-mode chorus waves preferred to occur in the inner magnetosphere?: Coupled MHD and advection simulations (2020)
  • Author(s): Ebihara, Y., T. Ikeda, Y. Omura and T. Tanaka
  • Organizer: VLF/ELF Remote Sensing of the Ionosphere and Magnetosphere (VERSIM) 2020
  • Int'l Joint Research / Invited
• [Presentation] Analysis on the auroral electrojet by numerical simulation (2020)
  • Author(s): Yano, Y. and Y. Ebihara
  • Organizer: American Geophysical Union Fall Meeting 2020
  • Int'l Joint Research
• [Remarks] 磁気嵐とオーロラの研究
  • URL: https://www.rish.kyoto-u.ac.jp/~ebihara/