Study on spatio-temporal variations of oxygen ring current enhancements during magnetic storms using multi-spacecraft observations

2019 Fiscal Year Annual Research Report

• Project/Area Number: 17K14400
• Research Institution: The University of Tokyo
• Principal Investigator: 桂華 邦裕 東京大学, 大学院理学系研究科(理学部), 助教 (10719454)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 環状電流 / 磁気嵐 / 地球起源酸素イオン

Outline of Annual Research Achievements

今年度は、交付申請書の「研究の目的」に記載した課題②および③について、Van Allen Probes衛星搭載のECT/HOPE粒子検出器で観測された低エネルギー（1 keV以下）水素イオンと酸素イオンについて、磁気嵐発生前の空間分布や時間変動を調査した。多くの場合でイオン量の時間変動が大きく、同時観測の解析から地方時方向の相違が大きいことも明らかになった。一方で、明瞭な空間的偏りや地磁気活動度依存性は見られなかった。これらの結果は、酸素イオンの内部磁気圏への供給は、サブストーム現象などに伴い、短時間でかつ局所的に発生していることを示唆している。酸素イオンの平均量と磁気嵐規模の間には、強い相関は見られなかった。酸素イオンが局所的に増加している時間帯の長さや増加領域の広さなど、磁気嵐の規模に関連する可能性がある要素についても、はっきりとした相関は見られなかった。

また、MMS衛星が磁気圏尾部を飛翔している際にHPCA粒子検出器で取得された低エネルギー（1 keV以下）水素イオンデータを用いて、近尾部プラズマシートにおけるプラズマ特性を調査した。酸素イオンは十分なカウント数が得られない領域、時間帯が多かったため、今回は利用しなかった。速度分布関数を2成分フィッティングすることで、プラズマシート起源の熱い成分と電離圏あるいは太陽風起源の冷たい成分に分け、それぞれ密度と温度の特性を調べた。密度温度特性から電離圏起源と思われるプラズマ群を同定することができ、それらは地球半径の約10倍より地球側で卓越し、約20倍以内のプラズマ特性に大きな影響を与えていることが明らかになった。

Research Products

• [Int'l Joint Research] Johns Hopkins Univ. Applied Physics Lab./University of New Hampshire/Southwest Research Institute(米国)
  • Country Name: U.S.A.
  • Counterpart Institution: Johns Hopkins Univ. Applied Physics Lab./University of New Hampshire/Southwest Research Institute
  • # of Other Institutions: 1
• [Journal Article] Comprehensive observations of substorm-enhanced plasmaspheric hiss generation, propagation, and dissipation (2020)
  • Author(s): Liu, N., Su, Z., Gao, Z., Zheng, H., Wang, Y., Wang, S., Y. Miyoshi, I. Shinohara, Y. Kasahara, F. Tsuchiya, A. Kumamoto, S. Matsuda, M. Shoji, T. Mitani, T. Takashima, Y. Kazama, B. Wang, S. Wang, C. Jun, T. Chang, S. W. Y. Tam, S. Kasahara, S. Yokota, K. Keika, T. Hori, and A. Matsuoka
  • Journal Title: Geophysical Research Letters Volume: 47 Pages: e2019GL086040
  • DOI: 10.1029/2019GL086040
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Statistical study on electron and ion temperatures in the near-Earth reconnection and magnetic pileup regions (2019)
  • Author(s): Watanabe, K., Keika, K., Hoshino, M., Kitamura, N., Saito, Y., Giles, B. L., & Paterson, W. R.
  • Journal Title: Geophysical Research Letters Volume: 46 Pages: 14223-14229
  • DOI: 10.1029/2019GL084837
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Eastward Propagating Second Harmonic Poloidal Waves Triggered by Temporary Outward Gradient of Proton Phase Space Density: Van Allen Probe A Observation (2019)
  • Author(s): Yamamoto, K., Nose', M., Keika, K., Hartley, D. P., Smith, C. W., MacDowall, R. J., et al.
  • Journal Title: Journal of Geophysical Research Volume: 124 Pages: 9904-9923
  • DOI: 10.1029/ 2019JA027158
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Strong diffusion of energetic electrons by equatorial chorus waves in the midnight-to-dawn sector (2019)
  • Author(s): Kasahara, S., Miyoshi, Y., Kurita, S., Yokota, S., Keika, K., Hori, T., et al.
  • Journal Title: Geophysical Research Letters Volume: 46 Pages: -
  • DOI: 10.1029/2019GL085499
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Cusp and nightside auroral sources of O+ in the plasma sheet (2019)
  • Author(s): Kistler, L. M., Mouikis, C. G., Asamura, K., Yokota, S., Kasahara, S., Miyoshi, Y., Keika, K. et al.
  • Journal Title: Journal of Geophysical Research Volume: 124 Pages: -
  • DOI: 10.1029/ 2019JA027061
  • Peer Reviewed / Int'l Joint Research
• [Journal Article] Statistical properties of molecular ions in the ring current observed by the Arase (ERG) satellite (2019)
  • Author(s): Seki, K., Keika, K., Kasahara, S., Yokota, S., Hori, T., Asamura, K., Higashio, N., Takada, M., Ogawa, Y., Matsuoka, A., Teramoto, M., Miyoshi, Y., and Shinohara, I.
  • Journal Title: Geophysical Research Letters Volume: 46 Pages: 8643-8651
  • DOI: 10.1029/2019GL084163
  • Peer Reviewed
• [Journal Article] EMIC waves converted from equatorial noise due to M/Q = 2 ions in the plasmasphere: Observations from Van Allen Probes and Arase (2019)
  • Author(s): Miyoshi, Y., Matsuda, S., Kurita, S., Nomura, K., Keika, K., Shoji, M., et al.
  • Journal Title: Geophysical Research Letters Volume: 46 Pages: 5662-5669
  • DOI: 10.1029/ 2019GL083024
  • Peer Reviewed
• [Journal Article] Meridional distribution of middle-energy protons and pressure-driven currents in the nightside inner magnetosphere: Arase observations (2019)
  • Author(s): Imajo, S., Nose', M., Kasahara, S., Yokota, S., Matsuoka, A., Keika, K., et al.
  • Journal Title: Journal of Geophysical Research Volume: 124 Pages: -
  • DOI: 10.1029/2019JA026682
  • Peer Reviewed
• [Journal Article] Characteristics of CME- and CIR-driven ion upflows in the polar ionosphere (2019)
  • Author(s): Ogawa, Y., Seki, K., Keika, K., & Ebihara, Y.
  • Journal Title: Journal of Geophysical Research Volume: 124 Pages: -
  • DOI: 10.1029/ 2018JA025870
  • Peer Reviewed
• [Journal Article] Statistical Study of Selective Oxygen Increase in High-Energy Ring Current Ions during Magnetic Storms (2019)
  • Author(s): K. Mitani, K. Seki, K. Keika, M. Gkioulidou, L.J. Lanzerotti, D.G. Mitchell, C. A. Kletzing, A. Yoshikawa, Y. Obana
  • Journal Title: Journal of Geophysical Research Volume: 124 Pages: -
  • DOI: 10.1029/2018JA026168
  • Peer Reviewed
• [Presentation] Ion Energization During Reconnection-driven Large-scale Injections in Saturn's Magnetotail: Cassini Observations (2020)
  • Author(s): K. Keika, P. C. Brandt, D. G. Mitchell, R. C. Allen, C. Paranicas, M. Kusterer, D. C. Hamilton, and S. Sakai
  • Organizer: Symposium on Planetary Sciences 2020
• [Presentation] Ion energization in the near-Earth magnetotail observed by Arase (2019)
  • Author(s): K. Keika, S. Kasahara, S. Yokota, M. Hoshino, K. Seki, T. Amano, L. M. Kistler, M. Nose', Y. Miyoshi, T. Hori, and I. Shinohara
  • Organizer: AGU Fall Meeting 2019
  • Int'l Joint Research
• [Presentation] Transport and energization of ionospheric ions in Earth's magnetotail: Recent multi-spacecraft observations (2019)
  • Author(s): K. Keika
  • Organizer: APPC 2019 14th Asia-Pacific Physics Conference
  • Int'l Joint Research / Invited
• [Presentation] Mass- and charge-dependent ion energization in Earth's magnetotail: Arase observations (2019)
  • Author(s): K. Keika, S. Kasahara, S. Yokota, M. Hoshino, K. Seki, T. Amano, L. M. Kistler, M. Nose', Y. Miyoshi, T. Hori, and I. Shinohara
  • Organizer: SGEPSS 2019 Fall Meeting
• [Presentation] Characteristics of ion kinetic energies dominating plasma pressure: Spatial distributions and mass dependence (2019)
  • Author(s): K. Keika
  • Organizer: Ion Composition of Sun-Earth System meeting 2019
  • Int'l Joint Research
• [Presentation] Warm proton populations in the magnetotail under quiet conditions: Statistical analysis based on two-component fits of distribution functions (2019)
  • Author(s): K. Keika, R. Asami, M. Hoshino, S. Fuselier, and MMS/HPCA team
  • Organizer: Ion Composition of Sun-Earth System meeting 2019
  • Int'l Joint Research
• [Presentation] Statistical study on warm plasma in the magnetotail based on two-component fits of distribution functions (2019)
  • Author(s): K. Keika, R. Asami, M. Hoshino, S. Fuselier, and MMS/HPCA team
  • Organizer: JpGU Meeting 2019
  • Int'l Joint Research
• [Presentation] Oxygen-proton differences in ion energies dominating plasma pressure: Dependence on storm phases and solar wind drivers (2019)
  • Author(s): K. Keika, S. Kasahara, S. Yokota, M. Hoshino, K. Seki, M. Nose', Y. Miyoshi, and I. Shinohara
  • Organizer: JpGU Meeting 2019
  • Int'l Joint Research
• [Presentation] Proton-Oxygen Differences in Energy Spectral Evolution During Large-scale Injections in Saturn's Magnetosphere (2019)
  • Author(s): K. Keika, P. C. Brandt, D.G. Mitchell, and S. Sakai
  • Organizer: SGEPSS 2019 Fall Meeting
• [Presentation] Spatio-temporal Evolution of Energy Spectra of Energetic Protons and Oxygen Ions During Large-scale Injections in Saturn's Magnetosphere (2019)
  • Author(s): K. Keika, P. C. Brandt, D. G. Mitchell, M. Kusterer, D. C. Hamilton, and S. Sakai
  • Organizer: Magnetospheres of Outer Planets 2019 Meeting
  • Int'l Joint Research