Slow shocks in the interplanetary medium

The production of MHD shock ensembles in the solar wind will, in general, result in slow forward and reverse shocks in addition to fast forward and reverse shocks and a contact discontinuity. As opposed to fast shocks, which last for an extended period of time, slow shocks disappear in two stages. As they propagate outward, they are first weakened until their relative Mach number becomes close to unity. At this point they start to recede as slow magnetosonic waves and will merge asymptotically with the contact discontinuity to create a tangential discontinuity. This analytical result is demonstrated by a numerical simulation of MHD shock wave propagation in the solar wind. Some of the observed tangential discontinuities are probably a result of this process.