Interaction between magneto-acoustic waves and magnetic fields

I will review recent progress in our understanding of how magneto-acoustic gravity waves interact with large magnetic flux concentrations, such as sunspots. It is well known that sunspots absorb energy from and change the phase speed of solar acoustic oscillations, f- and p-modes, incident upon them. Time-distance helioseismology has also revealed that mean travel times are reduced for waves propagating into or away from the umbra of sunspots. I will discuss how these effects can be interpreted in terms of wave coupling, where acoustic waves in the nonmagnetic environment couple to m agneto-acoustic waves inside the magnetic region. I will also comment on the correspondence between modal and time-distance formulations of the wave coupling problem. It turns out that both of these approaches lead to consistent observational predictions that could be used to test our present interpretation of oscillations in and above sunspots in terms of wave coupling.