NONEVOLUTIONARY DISCONTINUOUS MAGNETOHYDRODYNAMIC FLOWS IN A DISSIPATIVE MEDIUM

Magnetohydrodynamic discontinuities in a dissipative medium are consid ered from the view point of the principle of evolutionarity. For a non evolutionary discontinuity, the problem of time evolution of a small p erturbation does not have a unique solution. This means that an infini tesimal perturbation results in finite variation of the initial flow. Such a discontinuity cannot exist as a stationary configuration and it must disintegrate or transform to some other nonsteady flow. Using th e kinematic properties of weakly damping high-frequency perturbations of a dissipative medium, the sufficient conditions of nonevolutionarit y of the dissipative discontinuities are obtained. These conditions ar e shown to strengthen the known criterion of a discontinuous profile o f inviscid shocks. It is suggested that time evolution of the nonevolu tionary shock that contains the nonevolutionary internal discontinuity is a superposition of two oscillation processes with different charac teristic times corresponding to internal disintegration and disintegra tion of the shock as a whole. (C) 1998 American Institute of Physics. [S1070-664X(98)03506-X]