[P-EM18] 磁気圏-電離圏ダイナミクス

[PEM18-06] サブストームの強度分布－双峰特性

*森岡 昭¹、三好 由純²、能勢 正仁³ (1.東北大学大学院理学研究科惑星プラズマ・大気研究センター、2.名古屋大学宇宙地球環境研究所、3.京都大学大学院理学研究科)

キーワード：サブストーム、強度分布、対数正規分布

One of the essential issues in substorm study is how is the substorm intensity distributed and what determines the distribution. In this study, the substorm intensity (AL index at substorm) distribution is statistically studied using the Wp index provided by WDC for Geomag, Kyoto University and OMNI data base. The results showed that substorm intensity distribution is composed of bi-modal peaks with lognormal distribution. The major peak is in small AL range around 100 nT (named group-S substorm) and the secondary peak is around 300 nT (named group-L substorm). The bi-modal distribution of substorm intensity means that substorm is not a continuum state between pseudo-substorms and full substorms as has been discussed. The solar cycle variation of the substorm intensity distribution showed that group-S substorms occure rather constantly during a solar cycle, whereas the appearance of group-L substorms is strongly dependent with the solar activity. These observations suggest that two different substorm processes are working in the magnetosphere or different solar wind-magnetosphere interaction processes are operating.