Solar wind entry via flux tube into magnetosphere observed by Cluster measurements at dayside magnetopause during southward IMF

Abstract

By analyzing hot ion and electron parameters together with magnetic field measurements from Cluster, an event of magnetopause crossing of the spacecraft has been investigated. At the latitude of about 40° and magnetic local time (MLT) of 13:20 during the southward interplanetary magnetic field (IMF), a transition layer was observed, with the magnetospheric field configuration and cold dense plasma features of the magnetosheath. The particle energy-time spectrograms inside the layer were similar to but still a little different from those in the magnetosheath, obviously indicating the solar wind entry into the magnetosphere. The direction and magnitude of the accelerated ion flow implied that reconnection might possibly cause such a solar wind entry phenomenon. The bipolar signature of the normal magnetic component BN in magnetopause coordinates further supported happening of reconnection there. The solar wind plasma flowed toward the magnetopause and entered the magnetosphere along the reconnected flux tube. The magnetospheric branch of the reconnected flux tube was still inside the magnetosphere after reconnection and supplied the path for the solar wind entry into the dayside magnetosphere. The case analysis gives observational evidence and more details of how the reconnection process at the dayside low latitude magnetopause caused the solar wind entry into the magnetosphere.