Coronal Heating and Solar Wind Acceleration by Alfven Wave Turbulence: A Global Computational Model and Observations.

Abstract

Alfven waves emanating from the chromosphere have been suggested as a possible driver of coronal heating and solar wind acceleration. Here, we explore whether Alfven waves can simultaneously predict the observed extreme ultraviolet (EUV) emission from the lower corona and the in-situ measurements of the solar wind. For the first time, a global magnetohydrodynamics (MHD) model driven by wave turbulence was developed. This model, the Alfven Wave Solar Model (AWSoM), extends from the top of the chromosphere up to 2 AU. It solves the two-temperature MHD equations coupled to wave transport equations. Wave pressure gradients accelerate the wind, while wave dissipation due to a turbulent cascade is the only heating mechanism. The strength of this new model is in the unified approach for describing wave dissipation in both open and closed field lines. The three-dimensional distribution of heating and acceleration rates that can explain both EUV and in-situ observations emerges naturally and self-consistently from this approach. We explored the transport of wave energy in the corona by producing synthetic emission lines from the model results. The line profiles, whose widths depend on the wave amplitude, were compared to spectral observations. We demonstrated that turbulent dissipation can simultaneously explain the observed heating rates and wave amplitudes in the lower corona. Wind acceleration was studied by simulating the ionization of heavy elements as they flow along open field lines. The emission due to the predicted charge states was calculated and compared to spectral observations up to a height of 1.16Rs above the limb. We found that the model cannot explain all the spectral observations at these heights; however, it can qualitatively reproduce and explain the large-scale variations in charge state composition observed in the slow and fast wind. Finally, the possible presence of supra-thermal electrons was shown to improve the agreement with both remote and in-situ observations. This work shows that turbulent Alfven waves can explain the large-scale structure of the corona, solar wind, and charge-state composition. The AWSoM model constitutes a major step toward a physics-based global solar model, and can improve our ability to predict space weather.