行星际日冕物质抛射中的磁流体波动观测

Magnetohydrodynamic waves in interplanetary coronal mass ejections near 1AU observed by WIND spacecraft

日冕物质抛射(CME)是最大尺度的太阳活动现象,灾害性空间天气的主要驱动源.行星际日冕物质抛射(ICME)中的等离子体波动性质与ICME的演化密切相关.由于ICME中的平均磁场较大,其中的Alfven低频扰动研究较少.前人的研究只分析了0.3AU和0.68AU处的个别ICME中的Alfven波动.ICME在1AU处的Alfven波观测较少.本文对第23太阳周1995–2006年期间所有引起大磁暴(Dst100nT)的单个ICME事件进行统计分析,结果表明:(1)大约30%的ICME中长时间存在Alfven波(超过ICME持续时间的30%);(2)约一半的ICME的鞘层中存在快磁声波;(3)所有ICME中都存在短时间段的慢磁声波.这些观测结果为研究CME在行星际传播过程时其中的Alfven波演化机制及其动力学演化提供了观测基础.

Previous observations of interplanetary coronal mass ejections （ICMEs） show that only from 0.3 to 0.68AU did Alfven wave exist in the ICMEs, and rarely discovered at 1AU in ICMEs. Here we present a preliminary statistical result on the existence of magnetohydrodynamic （MHD） waves in ICMEs near 1AU. Based on all of 27 single ICME events which led to major magnetic storms during 1996-2005, several types of MHD waves in ICMEs are identified with the dispersion relations by SVD method： （1） in about 1/3 ICMEs near 1AU, 8 out of 27 events, some Alfven waves exist continuously ; （2） in 13 cases there are fast waves exist in the sheath of the ICMEs; （3） slow waves exist in all events. These observations may show some new clues to the basic wave property and dynamics of ICME.