CORONAL HEATING AND SOLAR-WIND ENERGY-BALANCE

In this paper we present a parameter study of a two-fluid and a one-fluid model of the solar wind where coronal heating and solar wind acceleration is treated as one problem. To study the energy balance in the corona/solar wind system, we consider a ''mechanical'' energy flux emanating from the Sun which is transferred to the coronal plasma as heat with a characteristic dissipation length of a few tenths of a solar radius. The mechanical energy flux adding energy to the coronal plasma as heat is varied, and the dissipation length of the mechanical energy flux and the fraction of the energy added to protons (electrons) are varied. The low heat conductivity in the proton gas and the relatively weak thermal coupling between electrons and protons cause large temperature differences in the corona. In two-fluid models with electron heating and in one-fluid models, a larger fraction of the mechanical energy flux is lost as heat conduction and radiation than in two-fluid models with pure proton heating. In all models where an energy flux is added to the quasi-static corona as heat, the asymptotic flow speed is low. We demonstrate how a flux of Alfven waves emanating from the Sun can accelerate the thermally driven solar wind to asymptotic flow speeds higher than the Sun's escape speed.