The formation of superdense plasma sheet in association with the IMF turning from northward to southward

Abstract : We have studied two events in which relatively superdense plasma appeared near geosynchronous orbit after the interplanetary magnetic field (IMF) changed from a long period of northward condition to southward condition. We used the magnetosphere MHD model Open Geospace General Circulation Model to simulate these two events and compared the simulation results with observations. The observations and the simulation results show that an extended period of northward IMF caused a cold dense plasma sheet (CDPS) to form in the near tail, and a subsequent southward IMF caused a highly stretched near-tail dipole field, which enhanced the earthward convection and eventually set off reconnection. Some of the cold dense plasma was thus consequently transported to geosynchronous orbit and formed a superdense plasma sheet (SDPS). CDPS is the main source of SDPS in its early stage after the IMF southward turning.