THE INFLUENCE OF MAGNETISM ON P-MODE SURFACE AMPLITUDES

We propose a mechanism to explain the observed suppression of p-mode s urface velocities in solar active regions. We show that a horizontal m agnetic held can lower the upper turning point and change the shin dep th for a simple plane-parallel adiabatically stratified polytrope. In addition to power suppression, the magnetic field alters the phase of p-modes. Simultaneous measurements of phase as well as amplitude in th e active and quiet regions would provide an additional diagnostic for probing the structure of active region magnetic fields.