WKB APPROACH TO THE PROBLEM OF MHD SHOCK PROPAGATION THROUGH THE HELIOSPHERIC CURRENT SHEET

The interplanetary shock wave front shape and intensity are calculated numerically by means of the WKB-approach, with nonlinear effects taken into account. The solar flare is modelled as an isotropic point explosion at the solar wind base. The heliospheric current sheet (HCS) is represented by a radially diverging stream with a higher plasma concentration and a lower wind speed. Fast magnetosonic shock wave propagation along the HCS is connected with the effect of regular accumulation of the wave energy in the vicinity of the HCS. In this place the wave intensity is increased, and the corresponding front fragments go ahead to form a shock-wave forerunner as a 'pimple'. The 'primple', in turn, is located inside a quite a large, but less-contrast, 'dimple' in the wave surface. This 'dimple' approximately coincides with the HCS stream contours. If the flare is outside the HCS boundaries, the picture discussed above is conserved, but asymmetry effects arise. Thus the interplanetary shock is stronger when the Earth's observer and the flare are on the same side of the HCS and is weaker in the opposite case.