Magnetohydrodynamic shock heating and solar wind acceleration at coronal holes

Magnetohydrodynamic waves are excited at the solar corona by perturbations to the magnetic field lines. These wave propagate upward in open field line configurations, carrying with them the energy from the excitation. Shocks form and part of the wave energy is converted to plasma heating and motion when the conditions are favorable. A numerical model is developed to accurately follow the shock formation and the subsequent energy release. This model includes an adiabatic energy equation for the explicit evaluation of the temperature increases and the energy fluxes contributed by the passing shock. Propagation through unstratified, as well as stratified media are considered. Transverse, plane polarized excitations are used; they can be periodic as in Alfven wave trains, or pulsed as might result from nanoflares. The results from the numerical simulations show that shocks form and important amounts of plasma heating and mass outflow may occur when nonlinear waves move along strong magnetic fields with low plasma beta, with field amplitudes comparable to the background field. Fast and slow magnetoacoustic shocks are generated; each one making its own contribution. Most of the heating takes place in the low corona, but long range distributed heating still occurs up to heights of several solar radii. The energy fluxes for the stronger cases is sufficient to compensate for thermal and convective losses at coronal holes, consistent with observations and theoretical models. It was concluded that large amplitude MHD shocks in low beta regions could be a viable mechanism for coronal heating and wind acceleration in regions of open magnetic field lines.