日本地球惑星科学連合2016年大会

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セッション記号 P (宇宙惑星科学) » P-EM 太陽地球系科学・宇宙電磁気学・宇宙環境

[P-EM04] Space Weather, Space Climate, and VarSITI

2016年5月22日(日) 15:30 〜 17:00 103 (1F)

コンビーナ:*片岡 龍峰(国立極地研究所)、プルキネン アンティ(NASAゴダード宇宙飛行センター)、海老原 祐輔(京都大学生存圏研究所)、三好 由純(名古屋大学宇宙地球環境研究所)、清水 敏文(宇宙航空研究開発機構宇宙科学研究所)、浅井 歩(京都大学宇宙総合学研究ユニット)、陣 英克(情報通信研究機構)、佐藤 達彦(日本原子力研究開発機構)、草野 完也(名古屋大学宇宙地球環境研究所)、宮原 ひろ子(武蔵野美術大学造形学部)、伊藤 公紀(横浜国立大学大学院工学研究院)、塩川 和夫(名古屋大学宇宙地球環境研究所)、中村 卓司(国立極地研究所)、余田 成男(京都大学大学院理学研究科地球惑星科学専攻)、一本 潔(京都大学大学院理学研究科附属天文台)、石井 守(国立研究開発法人情報通信研究機構)、座長:Pulkkinen Antti Aleksi(The National Aeronautics and Space Administration)

16:40 〜 17:00

[PEM04-21] Substorm simulation: Current system and auroral structure

★招待講演

*海老原 祐輔1、田中 高史2 (1.京都大学生存圏研究所、2.九州大学 国際宇宙天気科学・教育センター)

キーワード：Substorm, Aurora, Geomagnetically Induced Current (GIC)

Substorm is known to cause strong geomagnetically induced current (GIC) on the ground in the polar region. The GIC is primarily caused by the ionospheric current that is intensified by field-aligned current (FAC) during the substorm. On the basis of the result obtained by a global magnetohydrodynamic (MHD) simulation, we propose a scenario for the evolution of the current system associated with a substorm expansion. (1) Near-Earth neutral line releases magnetic tension in the near-Earth plasma sheet to compress plasma and accelerate it earthward. (2) Earthward, perpendicular flow is converted to parallel flow when flow braking takes place. (3) Plasma moves earthward parallel to a field line. The plasma pressure is additionally enhanced at off-equator. (4) Flow vorticities coexist near the off-equatorial high-pressure region. Resultant FAC is connected to the ionosphere, which may manifest initial brightening of aurora. The ionospheric current starts to increase. (5) Due to continued earthward flow, the high-plasma pressure region continues to expand to the east and west. (6) The ionospheric conductivity continues to increase in the upward FAC region, and the conductivity gradient becomes steeper. (7) The convergence of the Hall current gives rise to divergent electric field near the steep gradient of the conductivity. (8) Due to the divergent electric field, magnetospheric plasma moves counterclockwise at low altitude (as seen in the Northern Hemisphere). (9) The additional flow vorticity generates a localized upward FAC at low altitudes, which may manifest westward traveling surge (WTS) of aurora. As a consequence, the ionospheric current, conductivity, and the magnetospheric current system are redistributed. The evolution of the substorm depends on the solar wind condition as well as the magnetospheric condition. We will discuss the optimal condition that potentially causes the strong substorm.