MAGNETOSHEATH PARAMETERS AND RECONNECTION - A CASE-STUDY FOR THE NEAR-CUSP REGION AND THE EQUATORIAL FLANK

We use the magnetohydrodynamic approach to calculate all plasma and ma gnetic field quantities along a line normal to the magnetopause, begin ning at the bow shock, through the magnetosheath and magnetopause, and into the magnetosphere. Our method is based on a perturbation calcula tion, where we expand in orders of 1/M(A infinity), with M(A infinity) the Alfven Mach number upstream of the bow shock. The calculations ar e carried out (1) in the noon-midnight meridian at latitudes just sout h of the northern cusp, and (2) in the equatorial flank region. Our ca lculations are for an interplanetary magnetic field (IMF) which is dir ected perpendicular to the upstream solar wind. We consider two orient ations of the IMF. In one case, the interplanetary field points due so uth, i.e. antiparallel to the magnetospheric field in the subsolar poi nt. In the second case, it lies in the equatorial plane and points fro m dusk to dawn. For each of these different orientations of the IMF, i n situ observations of reconnection have been made. In the magnetoshea th region adjacent to the magnetopause, i.e. in the so-called magnetic barrier, the magnetic forces react back on the plasma flow. This effe ct is included consistently in the calculation by the use of a special coordinate system. The magnetic field tension accelerates the plasma in a direction perpendicular to the held and thus the magnetic field p roduces an asymmetry in the flow held. At the magnetopause we describe shock-type reconnection, taking as input on the magnetosheath side th e results of the above calculation and taking at the magnetospheric si de typical values for the outer boundary of the magnetosphere. The for mat in which the results are presented is similar to that used in the presentation of bulk parameters and magnetic held measurements obtaine d from spacecraft.