[P-EM13] 内部磁気圏

[PEM13-25] Multiple Satellite Observations of Oxygen Torus in the Inner Magnetosphere

*能勢 正仁¹、松岡 彩子²、熊本 篤志³、笠原 禎也⁴、Goldstein J^5,6、寺本 万里子¹、土屋 史紀³、松田 昇也²、小路 真史¹、今城 峻¹、生松 聡⁷、山本 和弘⁷、尾花 由紀⁸、野村 麗子⁹、藤本 晶子¹⁰、篠原 育²、三好 由純¹、Kurth S¹¹、Kletzing C¹¹、Smith C¹²、MacDowall R¹³ (1.名古屋大学宇宙地球環境研究所、2.宇宙航空研究開発機構宇宙科学研究所、3.東北大学大学院理学研究科、4.金沢大学総合メディア基盤センター、5.Space Science and Engineering Division, Southwest Research Institute、6.University of Texas at San Antonio、7.京都大学大学院理学研究科、8.大阪電気通信大学工学部、9.国立天文台、10.九州工業大学、11.Department of Physics and Astronomy, University of Iowa、12.Institute for the Study of Earth, Oceans, and Space, University of New Hampshire、13.Solar System Exploration Division, Goddard Space Flight Center)

A recent study employing the Arase and Van Allen Probes A satellites at different MLT revealed an event in which the inner magnetospheric O⁺ density enhancement (know as the dense oxygen torus) does not extend over all MLT. Rather, the torus is skewed toward the dawn sector, being described more precisely as a crescent-shaped torus or a pinched torus [Nosé et al., 2018]. In the reported event of 24 April 2017, Arase flying in the morning sector detected an enhancement of the average plasma mass up to ~3.5 amu around L=4.9–5.2, while Van Allen Probe A flying in the afternoon sector observed no clear enhancements in the average plasma mass. In the present study, we focus on simultaneous observations of the magnetic field and plasma waves made by the Arase and Van Allen Probes A and B satellites on 12 September 2017. For this event the orbital configuration of the satellites is opposite to that in the study by Nosé et al. [2018]; that is, Arase is in the afternoon and the Van Allen Probes are in the morning. It is found that only Probe B observed a clear enhancement in the average plasma mass up to ~4 amu around L=3.5 and MLT=9.0 hr. This result demonstrates that the crescent-shaped O⁺ torus is not a unique (single-event) occurrence, and thus may be a general feature of the density enhancement in the inner magnetosphere.