异常SSC事件的行星际原因分析

The Interplanetary Causes of the Anormalous SSC Events

磁暴急始(SSC)是强烈太阳风动压或行星际激波与磁层相互作用的结果．通常SSC事件的上升时间在4～10 min,我们把上升时间超过15 min的SSC事件称为异常SSC事件．本文利用地磁SYM-H指数鉴别出了5个有地磁观测历史以来发生的上升时间大于15 min的异常SSC事件,并利用Wind,ACE,IMP8, Goes,Geotail多点卫星太阳风观测数据和地磁观测数据,分析了异常SSC事件的行星际原因．结果表明,异常SSC事件通常都是强烈行星际扰动引起的,5个异常SSC事件有4个对应于行星际激波,有3个对应于多步太阳风动压跃变,有1个对应于行星际电场大幅度变化;由行星际激波产生的异常SSC事件,其上升时间依赖于行星际激波的方向,方向相对于日地连线越偏,上升时间越长;异常SSC事件上升时间与行星际磁场方向关系不明显．

SSC is a result of the interrelation between strong solar wind dynamic pressure or interplanetary shock and the geomagnetosphere. Generally, the rise time of SSC varies from 4 minutes to 10 minutes. So, we refer to the SSC of the rise time which is more than 15 minutes as anomalous SSC event. We identified 5 anomalous SSC events from the geomagnetic index SYM-H data since the observation beginning of the geomagnetic field. Using the multipoint observations of the solar wind from the Wind, ACE, IMP 8, Goes and Geotail, the interplanetary causes of those anomalous SSC events were analyzed. It is found that： （1） all of 5 anomalous SSC events are accompanied with strong interplanetary disturbances, among which there are 4 events corresponding with the forward fast interplanetary shocks, and 3 events corresponding with multi-step solar wind dynamic pressure changes and 1 event corresponding with a sudden direction change and large amplitude variation in interplanetary electric field. （2） the rise time of those resulted from interplanetary shocks desponds on the orientation of the interplanetary shock, i.e., the bigger the angle between the interplanetary shock normal and the Sun-Earth line, the shorter the rise time, and the contribution of the orientation of the interplanetary shock is more remarkable than its speed. （3） There is no explicit relation between the rise time of the anomalous SSC events and the interplanetary field direction.