  We suggest an explanation for the high-frequency power excess surrounding
active regions known as seismic halos. The idea is based on numerical
simulations of magneto-acoustic waves propagation in sunspots. We propose that
such an excess can be caused by the additional energy injected by fast mode
waves refracted in the higher atmosphere due to the rapid increase of the
Alfven speed. Our model qualitatively explains the magnitude of the halo and
allows to make some predictions of its behavior that can be checked in future
observations.
