Structure of the reconnection layer at the dayside magnetopause

Abstract

A two-dimensional compressible MHD simulation is carried out to study the structure of the reconnection layer at the dayside magnetopause. In particular, this paper investigates systematically the effects of three parameters on the reconnection layer structure. These three parameters are the ratio of the plasma densities and the ratio of the magnetic field strength magnitudes on the two sides of the initial current sheet and the plasma β. In a symmetric configuration, the reconnection layer is found to be bounded by a pair of slow shocks as predicted in Petschek's model. However, under the asymmetric conditions typical of the dayside magnetopause, the reconnection layer is found to be bounded by an intermediate shock on the magnetosheath side and a weak slow shock on the magnetospheric side. Contact discontinuities and slow expansion waves can also be identified in the reconnection layer in some simulation cases. In the presence of a large β, the slow shocks or the intermediate shocks in the reconnection layer become weaker. Finally, it is suggested that the development of the intermediate shock in the reconnection layer at the dayside magnetopause may be attributed to the large difference in the Alfvén speeds on the two sides of the dayside magnetopause.