Absolute and convective instability of tangential discontinuities in viscous fluids: Application to heliopause

The stability of the heliopause, which is a tangential discontinuity separa ting the flow of the solar wind plasma compressed at the termination shock, from the flow of the insterstellar plasma compressed at the bow shock, is discussed. A brief review of the normal mode analysis is given. The recent results of the study of the absolute and convective instability of a tangen tial discontinuity in an incompressible plasma, viscous at one side of the discontinuity, and ideal at the other side, are presented. This equilibrium configuration can be considered as a crude model of the flow near the heli opause in its near-flank regions, where the flow is essentially subsonic. T he obtained results suggest that the near flanks of the heliopause are only convectively unstable. The relation of these results with results of recen t numerical investigations of the absolute and convective instability of th e heliopause are discussed.