[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P02] Arase observations of field and plasma characteristics in the source region of a storm-time auroral brightening arc

*Chen Liwei¹、塩川 和夫¹、三好 由純¹、大山 伸一郎^1,2、Jun Chae-Woo¹、小川 泰信²、細川 敬祐³、風間 洋一⁵、Wang Shiang-Yu⁵、Tam Sunny Wing-Yee⁴、Chang Tzu-Fang^1,4、Wang Bo-Jhou⁵、浅村 和史⁶、笠原 慧⁷、横田 勝一郎⁸、堀 智昭¹、桂華 邦裕⁷、笠羽 康正⁹、熊本 篤志⁹、土屋 史紀⁹、小路 真史¹、笠原 禎也¹⁰、松岡 彩子¹¹、篠原 育⁶、今城 峻¹¹ (1.名古屋大学宇宙地球環境研究所、2.国立極地研究所、3.電気通信大学、4.国立成功大学宇宙プラズマ科学研究所、5.中央研究院天文及天文物理研究所、6.宇宙航空研究開発機構宇宙科学研究所、7.東京大学、8.大阪大学、9.東北大学、10.金沢大学、11.京都大学大学院理学研究科地磁気世界資料解析センター)

キーワード：サブストーム、オーロラ、内部磁気圏

Since the plasma and electromagnetic conditions can be very different with quiet time during geomagnetic storm, there will be differences between substorms that occur during geomagnetic quiet time and storm time. In this presentation, we show a unique auroral substorm study during a geomagnetic storm using a ground-based all-sky camera and the Arase satellite at L~6. The auroral arcs of interest were observed on September 8, 2017, at Tromsø, Norway (69.6^oN, 19.2^oE, in geographic coordinates; 66.7°N in geomagnetic coordinates). The ground-based electron-multiplying charge-coupled device (EMCCD) camera observed that the auroral arcs in the south edge of field-of-view (FOV) started their poleward expansion at ~2040 UT, while the footprint of the Arase satellite was moving southeastward and crossed the poleward-expanding arc at the southwestern edge of FOV at ~2043 UT. The Dst index indicates that this substorm occurred during the recovery phase of a geomagnetic storm with a minimum Dst of -122 nT at 0200 UT on September 8. The ion and electron energy spectra from the Arase on-board omnidirectional particle measurements show clear ion and electron flux enhancements before and at the timing of the footprint crossing of the poleward-expanding aurora. A series of field-aligned Poynting flux enhancements were found to appear simultaneously with the ion and electron flux enhancement. The magnetic field data suggest the existence of field-aligned current (FAC) when the satellite footprint crosses the poleward-expanding arc. From these observations, we suggest that a pressure gradient at high magnetic latitudes in the inner magnetosphere contributes to the formation of FAC and the auroral poleward expansion. In the presentation, we will also discuss these results with previous conjugate observations of substorm auroral brightening during geomagnetically quiet time, in light of differences of magnetospheric processes between quiet-time and storm-time substorms in the inner magnetosphere.