STANDING SHOCKS IN A 2-FLUID SOLAR-WIND

We present a numerical study of the formation of standing shocks in th e solar wind using a two-fluid time-dependent model in the presence of Alfven waves. Included in this model is the adiabatic cooling and the rmal conduction of both electrons and protons. In this study, standing shocks develop in the flow when additional critical points form as a result of either localized momentum addition or rapid expansion of the flow tube below the existing sonic point. While the flow speed and de nsity exhibit the same characteristics as found in earlier studies of the formation of standing shocks, the inclusion of electron and proton heat conduction produces different signatures in the electron and pro ton temperature profiles across the shock layer. Owing to the strong h eat conduction, the electron temperature is nearly continuous across t he shock, but its gradient has a negative jump across it, thus produci ng a net heat flux out of the shock layer. The proton temperature exhi bits the same characteristics for shocks produced by momentum addition but behaves differently when the shock is formed by the rapid diverge nce of the flow tube. The adiabatic cooling in a rapidly diverging flo w tube reduces the proton temperature so substantially that the proton heat conduction becomes negligible in the vicinity of the shock. As a result, protons experience a positive jump in temperature across the shock. While Alfven waves do not affect the formation of standing shoc ks, they contribute to the change of the momentum and energy balance a cross them. We also find that for this solar wind model the inclusion of thermal conduction and adiabatic cooling for the electrons and prot ons increases significantly the range of parameters characterizing the formation of standing shocks over those previously found for isotherm al and polytropic models.