[P-EM13] Dynamics of the Inner Magnetospheric System

[PEM13-P14] The inner edge location of SAPS electric field and the ring current in the equatorial magnetosphere as observed by Arase and SuperDARN

*堀 智昭¹、三好 由純¹、中村 紗都子¹、笠羽 康正²、中川 朋子³、北原 理弘²、松田 昇也⁴、西谷 望¹、Shepherd S. G.⁵、Ruohoniemi J. M.⁶、熊本 篤志²、土屋 史紀²、笠原 禎也⁴、浅村 和史⁷、Jun Chae-Woo¹、風間 洋一⁸、Wang S.-Y.⁸、Tam Sunny, W. Y.⁹、桂華 邦裕¹⁰、笠原 慧¹⁰、横田 勝一郎¹¹、松岡 彩子¹²、篠原 育⁷ (1.名古屋大学宇宙地球環境研究所、2.惑星プラズマ・大気研究センター、3.東北工業大学、4.金沢大学、5.ダートマス大学、6.バージニア工科大学、7.宇宙航空研究開発機構、8.台湾中央研究院、9.台湾成功大学、10.東京大学、11.大阪大学、12.京都大学地磁気世界資料センター)

Electric field (E-field) enhancement of subauroral polarization streams (SAPS) and associated particle boundaries in the inner magnetosphere is extensively investigated by analyzing particle and field data obtained by the Arase satellite and ionospheric convection data obtained by Super Dual Auroral Radar Network (SuperDARN). A previous study using Arase and SuperDARN revealed that there are two types of the SAPS events in terms of the spatial correspondence with the ring current: (type A) the inner edge location of SAPS matches with that of the ring current in some cases, while, (type B) in some other cases, their inner edge locations do not match well, and the ring current appears to extend further inward from SAPS. To address why these two types of spatial relationship occurs and what condition controls them, we statistically examined their correlation with substorm activity. Our statistical study indicates that almost all the type-B SAPS events are accompanied by some preceding substorm activity including intermittent occurrence of multiple substorms. This result suggests that a ring current portion located inward of SAPS has been injected by preceding substorms. Such a fossil population drifts around the Earth for some time and its azimuthal pressure gradient would be smeared out, unable to drive downward field-aligned current and thus SAPS. In contrast to type-B, we do not find a clear-cut tendency about the type-A events: they occur either during isolated substorms after prolonged (~several hours) quiet periods, or during a substorm preceded by separate ones. We speculate that these conditions somehow create a relatively simple structure of injected ions at its inner edge, leading to a smaller separation of SAPS inner edge.