DOPPLER ACOUSTIC DIAGNOSTICS OF SUBSURFACE SOLAR MAGNETIC-STRUCTURE

We used the Bartol-NSO-NASA South Pole helioseismic observations of 19 91 January to probe the subsurface structure of active regions to dept hs of similar to 15,000 km. The helioseismic signature we particularly examine is intended to register acoustic Doppler effects caused by ho rizontal flows associated with the active region. We propose to show t hat the Doppler acoustic signature of horizontal flows is particularly well suited for deep subsurface diagnostics in terms of vertical disc rimination of the structure. This study is based primarily on observat ions of NOAA Active Regions 6431, 6432, 6440, and 6442 between 1991 Ja nuary 1 and January 8. We interpret the acoustic signatures we find in terms of a general outflow of the solar medium surrounding the active region. The acoustic signatures are strongly dependent on wavenumber, which suggests an outflow that is quite weak near the surface, the up per 4000 km of the subphotosphere, bur which increases strongly with d epth to velocities of several hundred meters per second at 15,000 km. This depth profile evolves rapidly as the active region matures. Young active regions show a strong outflow signature for waves that explore depths between 4000 and 8000 km. As the active region matures, the ou tflow vacates these intermediate layers and submerges to depths mostly below 8000 km. We examine the location of AR 6442 for a possible pree mergence signature. We also show evidence for extended, relatively sup erficial flows in the quiet Sun between the active region bands direct ed roughly into the active region bands.