A new axisymmetric MHD model of the interaction of the solar wind with Venus

A new two-dimensional axisymmetric MHD model is used to study the interaction of the solar wind with Venus under conditions where tile interplanetary field is approximately aligned with the solar wind velocity. This numerical model solves the MHD transport equations for density, velocity, pressure, and magnetic field on an adaptively refined, unstructured grid system. This use of an adaptive grid allows high spatial resolution in regions of large density/velocity gradients and yet can be run on a workstation. The actual grid sizes vary from about 0.06 R(v) near the bowshock to 2 R(v) in the unperturbed solar wind. The results of the calculations are compared with observed magnetic field values obtained. from the magnetometer on the Pioneer Venus Orbiter, at a time when the angle between the solar wind velocity vector and the interplanetary magnetic field (IMF) was only 7.6 degrees Good qualitative agreement between the observed and calculated field behavior is found. The overall results suggest that the induced magnetotail disappears when the IMF is radial for an extended time period and implies that it weakens when the field rotated through a near-radial orientation.