The thickness of resistive‐dispersive shocks

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 λ r and the ion inertial length λ i . It is found that for the case where λ r ≪ λ i , 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 λ r ≫ λ i , 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 λ i . Thus a minimum thickness is predicted by the resistive‐dispersive model and occurs for intermediate resistivity: it is found to be a few λ i for the slow shocks in distant magnetotail as well as for subcritical bow shocks and about 20λ i for intermediate shocks with typical magnetopause parameters. It is shown that the shock thickness also depends critically on the upstream plasma beta, β 1 = 2μ o p 1 / B 1 ², small β 1 values leading to smaller thickness. The effect of regular Newtonian viscosity on the shock thickness is also examined briefly.