磁鞘快速流引起的磁层顶凹陷事件

Recent studies indicated that the magnetopause indentation plays an important role in magnetosphere-ionosphere coupling. Confirmation of magnetopause indentation requires joint observations with multiple satellites. So far, there have been few magnetopause indentation events reported. In this paper, a case of magnetopause indentation induced by fast magnetosheath flow is reported with multiple spacecraft analysis based on the observations of five THEMIS probes. During the interval from 10:00UT to 10:45UT on 21 July 2007, when the five THEMIS probes are located near the subsolar magnetopause, a fast anti-sunward flow (with a velocity of 400 km·s⁻¹) was observed in the magnetosheath just before THEMIS crossed the magnetopause to the magnetosphere. A magnetopause local indentation event was identified by comparing the nominal magnetopause and the tangential magnetopause plane calculated using the MVA method. In order to explore the origin of this magnetosheath fast flow, solar wind data observed by WIND satellite at L1 point were analyzed. It is found that the solar wind is very stable during this period. The Interplanetary Magnetic Field (IMF) is mainly radial and the component of the north-south direction is very small. It is speculated that the generation of this magnetosheath fast anti-sunward flow may be related to the radial IMF.