Influence Of Solar Wind Speed And Heliospheric Current Sheet On The ICMEs Transit Time

The table of 88 CME events that cause significant geomagnetic storms in the paper of Zhang et al, table of 47 CME events and table of 27 Full Halo CME events in the paper of Gopalswamy are used along with the WIND spacecraft observations of interplanetary solar wind and ICME at 1AU and the magnetic graph on the solar photosphere assembled by Wilcox Solar Observatory (WSO) to analyze the effect of various conditions of ambient solar wind speed and heliospheric current sheet on the ICME transit time to the earth. The results show that the ambient solar wind speed and the ICME transit time errors show little correlation, even after taking into account the angle of magnetic cloud flux tube to the ecliptic plane the correlation is still not obvious. However, the heliospheric current sheet shows significant influences on the ICME transit time. For the CMEs with relatively small initial velocity, the transit time of the opposite side events (if the earth and the source of CME are on the opposite side of the current sheet we call this a opposite side event, otherwise it is called a same side events) are longer than that of the same side events. For CMEs with large initial velocity, the transit time of the opposite side events are shorter than that of same side events. The result is totally 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 require further study.