Seismic Imaging of Acoustic Moats around Active Regions
Abstract
Phase-correlation statistics comparing acoustic radiation coming out of a particular point on the solar photosphere with acoustic radiation going into it show considerably reduced sound travel times through the subphotospheres of active regions. This is already well established by scattering phase shifts of single sunspots by Braun and Fan, and by time-distance correlations measured by Duvall et al. We have now applied techniques in phase-sensitive seismic holography to obtain high resolution phase-correlation maps of active regions and the "acoustic moats" that surround them. Correlation maps obtained for several active regions show that the seismic perturbation manifested by the acoustic moats extends 30 Mm or so beyond the visible sunspots, and in large active-region complexes is quite predominate. Indeed, the acoustic moat surrounding the large active region complex NOAA AR 8179 (1998 March 15) manifests a one-way travel-time reduction of approximately 30s over an area of some 10,000 sq. Mm, encompassing all of the significant sunspots in the region. Onto this phase perturbation the major sunspots impose an additional localized contribution of about 30s. These results strongly reinforce an interpretation of the acoustic moat as a well integrated convection cell driven by the thermal perturbation that results from the local blockage of convective heat transport by the sunspot photosphere.
- Publication:
-
SOHO-9 Workshop on Helioseismic Diagnostics of Solar Convection and Activity
- Pub Date:
- 1999
- Bibcode:
- 1999soho....9E..46B