MOTION OF THE HELIOSPHERIC TERMINATION SHOCK .4. MHD EFFECTS

In this paper we generalize earlier gasdynamic analyses of the motion of the heliospheric termination shock in response to upstream disturba nces (Barnes, 1993, 1994; Naidu and Barnes, 1994), to include magnetoh ydrodynamic (MHD) phenomena. We assume that the termination shock is a strong, perpendicular shock and that the initial upstream disturbance is a tangential discontinuity. The resulting configuration after the interaction is very similar to that in the gasdynamic models after an interaction with a contact discontinuity or interplanetary shock, and for an increase (decrease) in dynamic pressure consists of an outward (inward) propagating termination shock and an outward propagating shoc k (MI-ID rarefaction wave) that carries the signal of the disturbance into the far downstream plasma. The plasma immediately behind the new termination shock is separated from the downstream signal by a tangent ial discontinuity. The results of the model show that the speed of the new termination shock depends mainly on the magnitude of the change i n dynamic pressure and are typically of order similar to 100 km/s, com parable to the results of the gasdynamic models.