中文摘要：

本文使用Cluster-C1卫星的CIS仪器和FGM仪器测量得到的质子通量数据和计算的β数据,判断Cluster卫星在地球磁尾不同位置位于等离子体片内的概率.使用2001—2004年7—11月的Cluster-C1数据,分别在行星际磁场南向和北向时,得出X〈-10RE区域内卫星位于等离子体片的概率在Y-Dz平面的分布图（Dz是卫星到中性片的距离）.通过对比行星际磁场南向和北向时的卫星位于等离子体片的概率的分布图,我们发现等离子体片在行星际磁场南向时比在行星际磁场北向时要薄,并且这个效应在磁尾晨昏两侧比在午夜附近明显,同时我们还发现等离子体片在晨侧比在昏侧厚.

英文摘要：

Magnetotail plasma sheet is the most active area in Earth′s magnetosphere.It has been found that the features of plasma sheet are controlled by the conditions of Solar wind and Interplanetary Magnetic Field（IMF）.Some previous statistical studies have found that some parameters of the plasma sheet are dawn-dusk asymmetric.But the thickness of the magnetotail plasma sheet near the Cluster spacecraft orbit and how they are influenced by the IMF is still unclear.In this paper,the probability of the Cluster-C1 satellite encountering the plasma sheet is examined statistically by utilizing the proton flux andβdata from the CODIF and FGM equipment on board the Cluster-C1.Using data from July to November of year 2001—2004,the distributions of the probability of the satellite in the plasma sheet are mapped on the Y-Dz plane（Dzdenotes the distance from the neutral sheet）during the southward and northward IMF periods,respectively.By comparison,we found that the plasma sheet is thinner during southward IMF periods than that during northward IMF periods.It is more obvious in the flank regions of the plasma sheet.We also found that the plasma sheet in the dusk side is thinner than that in the dawn side.