Numerical Modelling of Shock Waves in the Solar Wind

Abstract

Abstract. This review briefly surveys some recent progress in the numerical simulation study of magnetohydrodynamic (MHD) shock waves in the solar wind. STANDING SHOCKS IN STEADY SOLAR W I N DIn order to accelerate the solar wind it is necessary to add energy or momentum to it. The energy or momentum addition creates more than one critical points, resulting in discontinuous solar wind solutions involving standing shocks [Holzer, 1977]. In terms of an isothermal model, Habbal and Tsinganos [1983] showed that multiple transonic solutions may exist for a given set of coronal base parameters owing to the presence of multiple critical points. One of these solutions is continuous while the others are all discontinuous, containing one or more standing shocks. Habbal and Rosner [1984] further examined the temporal evolution of an isothermal solar wind from one steady state to another under the action of momentum addition, and concluded that the pattern of the final steady state depends on the amplitude and the rate of momentum addition. This conclusion also holds for the polytropic solar wind [Habbal 1985]. Using a two-fluid model, Habbal et al. [1994] found a solar wind solution with two standing shocks. These studies indicate that solar winds with standing shocks are not only allowed by the steady state equations, but also physically accessible and stable. The presence of standing shocks bring about a remarkable change of the inner solar wind structure, which could be observationally detected [Esser and Habbal, 1990]. The transversal nonuniformity of the interplanetary magnetic field provides another physical basis for the formation of standing shocks. Whang [1982, 1986] suggested that a slow shock develops at the inner edge of the heliospheric current sheet and extends polewards to form a close surface around the Sun, and showed a typical solar wind solution with the close slow shock. If the prediction of discontinuous solar winds turns out to be confirmed by future observations, it will certainly bring about a revolution in the solar wind theory.A great upsurge in the study of the heliospheric boundary started several years ago and has since maintained since one or more of the deep space