The thickness of resistive‐dispersive shocks

Abstract

The purpose of this paper is to examine the thickness of slow, intermediate, and fast shocks described by the resistive‐dispersive plasma model, which contains two scale lengths: the resistive length λr and the ion inertial length λi. It is found that for the case where λr ≪ λi, i.e., for small resistivity, slowly damped wave trains dominate the structure yielding an effective shock thickness much greater than the ion inertial length. When λr ≫ λi, i.e., for large resistivity, the shock structure has a thickness of the order of the resistive length so that it is again much larger than λi. Thus a minimum thickness is predicted by the resistive‐dispersive model and occurs for intermediate resistivity: it is found to be a few λi for the slow shocks in distant magnetotail as well as for subcritical bow shocks and about 20λi for intermediate shocks with typical magnetopause parameters. It is shown that the shock thickness also depends critically on the upstream plasma beta, β1 = 2μop1/B1², small β1 values leading to smaller thickness. The effect of regular Newtonian viscosity on the shock thickness is also examined briefly.