INTERBALL-1 plasma sheet encounters and three-dimensional MHD modeling results

Abstract

We use magnetic field observations by the fluxgate magnetometer FGM-I during two substorm related INTERBALL-1 plasma sheet encounters to discuss signatures of reconnection in the Earth's magnetotail. In the first case the satellite stayed northward of the current sheet; in the second case for most of the substorm time it stayed in the northern lobes until it approached the plasma sheet and, finally, crossed the current sheet. In order to determine whether the observed magnetic field signatures can be understood in the framework of a resistive magnetohydrodynamic (MHD) approach to reconnection, we generated data using a three-dimensional numerical MHD model of the tail. In the model, reconnection takes place due to a localized finite resistivity. Comparing the modeled data with the measured ones, we find that, although the substorm-related dipolarization-like evolution of the B x and the B z field components can be well understood in terms of a resistive MHD approach to reconnection with dipolarization starting before the substorm ground onset and geostationary injection tailward of the satellite position, all attempts failed to explain the observed transient dawnward drop of the shear component B y by a resistive MHD model of three-dimensional reconnection. We conclude that the dawnward drop has to be caused by effects beyond the resistive MHD approach.