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

88 CME events that cause significant geomagnetic storms, 47 CME events and 27 Full Halo CME events, along with the ACE spacecraft observations of interplanetary solar wind and ICME at 1AU, 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.