Recent observational evidence for magnetic field direction effects on helioseismic signals in sunspot penumbrae is suggestive of magnetohydrodynamic

Using a newly developed extension of ray theory which accounts for mode transmission and conversion between fast and slow magnetoacoustic waves, as well as simple wave mechanical calculations, we find that strong surface magnetic fields, as may be found in solar and stellar active regions, have several related but distinct effects on seismic waves: transmission/conversion, shortened travel times, a directional filtering of acoustic waves entering the overlying atmosphere, and a tendency to more closely align velocities with the field as height increases in the atmosphere. Magnetic field inclination is particularly relevant to these effects. Here, we briefly review these findings, and present some new results on ray travel times and magnetic filtering.