Statistical research on the motion properties of the magnetotail current sheet: Cluster observations

The origin of the flapping motion of the earth's magnetotail current sheet is one of the most important problems in the magnetotail dynamics. Using Cluster data, we make a statistical research on the motion properties of the magnetotail current sheet of 2001 and 2003. We calculate the velocities of the magnetotail current sheet using new methods and obtain the distribution of the magnetotail current sheet velocities in the X-Y plane in GSE coordinate system. Our results show that although most of the current sheets were propagating toward the tail flanks and those of the exceptions lay in dusk side, which is consistent with previous studies, the proportions of the current sheet which were propagating toward midnight (where |Y (GSE)|=0) were higher than those in previous studies. Motions of the current sheet in the middle area (|Y (GSE)|< 8 Re) of the magnetotail are investigated. Relatively high value of the Z component of the velocity further confirms that the middle area of the magnetotail might be a source region for the motion of the current sheets which were propagating towards the tail flanks. According to our case studies, the way the current sheets propagated toward midnight area differs significantly from that toward dusk and dawn side, from which we infer that there might be two different kinds of current sheet motions originated from different sources. The statistical results of this paper may give some clues for further studies on the origin of the flapping motion of the magnetotail current sheet.