A statistical study of the plasma sheet in the near and middle earth magnetotail

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-Cl satellite encountering the plasma sheet is examined statistically by utilizing the proton flux and beta data from the CODIF and FGM equipment on board the Cluster-Cl. 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 (Dz denotes 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.