PROPAGATION AND EVOLUTION OF INTERPLANETARY SLOW SHOCK

Using a two-dimensional, ideal MHD model, this paper investigates the evolution of a slow shock in the solar wind in the heliospheric equatorial plane （2-D, 2-component model） and the heliospheric meridional plane （2-D, 3-component model） respectively. It is shown that the slow shock evolves into a shock system that consists of the original slow shock and a newly formed fast shock. The shock system is nearly symmetrical with respect to the central normal of the slow shock source in the heliospheric meridional plane, whereas it is asymmetrical in the heliospheric equatorial plane. There exists a touch point between the fronts of fast and slow shocks, at which the two shocks merge and degenerate into a gas-dynamic shock. The touch point deviates eastward with respect to the central normal of the shock source, and the deviation angle increases during the outward propagation of the shock system. A preliminary analysis shows that the east-west asymmetry of the propagation and evolution of the slow shock in the heliospheric equatorial plane is mainly attributed to the spiral structure of the interplanetary magnetic field.