Helioseismic Images of an Active Region Complex

Abstract

Helioseismic images of a large active region complex at a frequency of 5 mHz show a prominent halo of acoustic emission, which we call the ``acoustic glory,'' surrounding the active region. This feature is remarkably intense and contains small-scale elements of concentrated seismic emission which cluster in strings in nonmagnetic regions. Subsurface images show condensations of acoustic deficit that appear to represent acoustic perturbations located in excess of 10 Mm beneath the photosphere. The analysis of this complex active region suggests that these features are common in the neighborhoods of large active regions and can appear tens of megameters horizontally separated from sunspots. We propose that acoustic condensations are the result of refraction or scattering by subsurface thermal or Doppler perturbations below active regions. The appearance of acoustic glories and condensations strongly suggests that complex active regions have acoustic properties that are fundamentally different from those of single isolated sunspots.