Compressible magnetopause reconnection

Abstract

A fluid model is analyzed which describes the process of magnetic field merging in a geometry where a compressible magnetized plasma impinges upon a uniform vacuum magnetic field. This two-dimensional model is of the type first proposed by Petschek and co-workers more than a decade ago. In the model the magnetopause consists of a rotational discontinuity, and the plasma boundary layer immediately inside the magnetopause forms a narrow wedge-shaped region terminated by a slow expansion fan. Numerical results are given for the case where the magnetosheath field is exactly antiparallel to the magnetospheric field. It is found that for moderate reconnection rates, i.e., for ratios of flow speed to Alfvén speed in the inflow less than 0.2, the angular width of the boundary layer is less than 2°, the magnetic field component perpendicular to the magnetopause is less than 5% of the ambient field, and the plasma speed in the boundary layer is in the range 500–1000 km/s.