Hydromagnetic gravity waves in the solar atmosphere

We show that Alfven gravity waves propagating in a gravitationally stratified atmosphere do not suffer damping as a result of the rate of working of the gravity drift current on the electric field of the waves. A self-consistent treatment involving conservation of total energy, Poynting's theorem, and the rate of working of the various drift currents on the electric field demonstrates that dissipation only arises from "real" dissipative processes such as ohmic heating or viscous effects; otherwise the system is adiabatic. We also outline the propagation properties of coupled small-amplitude hydromagnetic gravity waves for the case of vertical and horizontal magnetic fields. In the latter case we discuss the phenomenon of critical level absorption, which can take place where the horizontal wave phase speed matches the Alfven speed at some height in the atmosphere.