太阳风速度及日球电流片对CME渡越时间的影响

Influence of Solar Wind Speed and Heliospheric Current Sheet on the CMEs Transit Time

基于1996—2005年88个引起重大地磁暴的CME(日冕物质抛射)事件、1996—2000年的47个CME事件以及1997—2002年的29个全晕状CME事件,结合ACE卫星在1 AU处的太阳风和行星际磁场观测资料以及Wilcox Solar Observatory(WSO)天文台的太阳光球层磁图,分析了背景太阳风速度和日球电流片对CME到达1 AU处渡越时间预报误差的影响.结果表明,背景太阳风速度与CME渡越时间误差并没有明显的相关性,在考虑了磁云通量管轴相对黄道面夹角的影响后相关性依然不明显.然而日球电流片对CME渡越时间却有明显的影响,对于初速度较小的异侧CME事件,其渡越时间大于同侧事件;而对于具有较大初速度的CME事件,异侧事件的渡越时间明显小于同侧事件.研究结果表明,CME与太阳风以及日球电流片的相互作用并不是简单的对流相互作用,造成高速CME异侧事件快于同侧事件到达地球的因素非常复杂,有待深入研究.

88 CME events that cause significant geomagnetic storms, 47 CME events and 27 Full Halo CME events, observation data of interplanetary solar wind and ICME measured by ACE spacecraft at 1 AU, as well as the magnetic graph on the solar photosphere assembled by Wilcox Solar Observatory （WSO）, are used to analyze the effect of various conditions of both ambient solar wind speed and heliospheric current sheet on the CME transit time to the Earth. The results demonstrate that the ambient solar wind speed and the CME transit time errors show little correlation, even after taking into account of the effect of the angle between magnetic cloud flux tube and the ecliptic plane. However, the heliospheric current sheet exerts significant influences on the CME transit time. For CMEs with relatively lower initial velocity, the transit time of the opposite side events is longer than that of the same side events （if the earth and the source of CME are on the opposite side of the current sheet it is called a opposite side event, otherwise it is called a same side event）. For CMEs with higher initial velocity, the transit time of the opposite side events is shorter than that of the same side events. The result is contrary to our expectations that the current sheet will impede the dissemination of ICMEs in the interplanetary space and thus extend the transit time. One possible explanation is that the interaction of CMEs with solar wind and the current sheet is not simply the convective interaction and the mechanism behind this phenomenon is very complex and requires further study.