Critical Mach numbers in classical magnetohydrodynamics

Abstract

Stationary point analysis is used to compute generalized critical Mach numbers for finite-amplitude fast and slow shocks in classical MHD fluids. Particular attention is paid to the case where the resistive and thermal conduction dissipation scale lengths are comparable and much larger than the viscous scale lengths. With both resistivity and thermal conduction, the critical Mach number at which viscosity must be invoked is determined by the condition that the downstream flow speed equals the isothermal sound speed. It is also shown that resistivity and thermal conduction can provide convergent stationary point solutions for nearly all slow shocks, except perhaps switch-off-shocks.