[P-EM16] Dynamics of Earth's Inner Magnetosphere and Initial Results from Arase

[PEM16-06] Magnetic field dipolarization and its associated ion flux variations in the deep inner magnetosphere: Arase and Michibiki-1 satellite observations

*能勢 正仁¹、松岡 彩子²、笠原 慧³、横田 勝一郎⁴、寺本 万里子⁵、桂華 邦裕³、野村 麗子⁶、藤本 晶子⁷、東尾 奈々⁶、越石 英樹⁶、今城 峻¹、田中 良昌⁸、篠原 学⁹、篠原 育²、三好 由純⁵ (1.京都大学大学院理学研究科、2.宇宙航空研究開発機構宇宙科学研究所、3.東京大学大学院理学研究科、4.大阪大学大学院理学研究科、5.名古屋大学宇宙地球環境研究所、6.宇宙航空研究開発機構つくば宇宙センター、7.九州大学国際宇宙天気科学・教育センター、8.国立極地研究所、9.鹿児島工業高等専門学校)

The Arase satellite observed clear dipolarization signatures at L~4.6–4.8 and magnetic local time (MLT)~5.5–5.7 h around 15:00 UT on 27 March 2017 when Dst~−70 nT. Strong magnetic field fluctuations were embedded in the dipolarization and their characteristic frequency was close to the local gyrofrequency of O⁺ ions. After the dipolarization, O⁺ flux was enhanced at 5–20 keV, while H⁺ flux showed no clear variations. These observations provide evidence for the selective acceleration of O⁺ ions by the magnetic fluctuations. At the same time, the Michibiki-1 satellite was located at L=6.6–7.1 and MLT=22.2–23.9 h. In four events out of six, magnetic field dipolarization was not identified at premidnight by Michibiki-1 but near dawn by Arase. This surprising MLT distribution of dipolarization in the inner magnetosphere may be attributed to an eastward skewing of partial ring current that is created during the storm main phase.