A New Method of Estimating the Magnetopause Speed of Motion

The magnetopause is the boundary where the solar wind and magnetosphere pressures balance each other. Once the upstream solar wind conditions change, the magnetopause moves to a new position and changes its shape accordingly. Previous studies usually calculate the speed of magnetopause motion from parameters of two crossings that were close in location and time. However, such events are relatively rare. A new hypothesis suggests application of the ion speed in the magnetopause layers to estimate the speed of magnetopause motion. As a boundary that plasma cannot pass through, the ion speed in the magnetopause should be related to the magnetopause speed. Our study aims to check whether this hypothesis is correct or not by using numerous magnetopause crossings recorded by the THEMIS mission. The magnetopause speed will be first calculated using the traditional method and compared with the results estimated using the new method.