THE ROLE OF HELIUM IN THE OUTER SOLAR ATMOSPHERE

We construct models of the outer solar atmosphere comprising the regio n from the mid-chromosphere and into the solar wind in order to study the force and energy balance in models with a significant helium abund ance. The corona is created by dissipation of an energy flux from the Sun. The energy flux is lost as radiation from the top of the chromosp here and as gravitational and kinetic solar wind energy flux. We find that in models with significant ion heating of the extended corona mos t of the energy flux is lost in the solar wind. The ion temperatures a re higher than the electron temperature in these models, and the alpha -particle temperature is much higher than the proton temperature, so t here is energy transfer from the alpha-particle fluid to the protons a nd electrons, but this energy exchange between the different species i s relatively small. To a fairly good approximation we can say that the energy flux deposited in the protons and alpha-particles is lost as k inetic and gravitational energy flux in the proton and alpha-particle flow. How this energy flux is divided between gravitational and kineti c energy flux (i.e., how large the particle fluxes and flow speeds are ) depends upon details of the heating process. We also find that mixin g processes in the chromosphere play an important role in determining the coronal helium abundance and the relative solar wind proton and al pha-particle fluxes. Roughly speaking, we find that the relative alpha -particle and proton fluxes are set by the degree of chromospheric mix ing, while the speeds are set by the details of the coronal heating pr ocess.