Authors: C. Lindsey, D.C. Braun
Affiliation: NorthWest Research Associates, Colorado Research Associates Division
Efforts to reconstruct phase-coherent helioseismic images of active region subphotospheres confront us with disproportionate phase perturbations introduced by strong magnetic fields in the upper few hundred km beneath the photosphere. These phase perturbations have an effect similar to that of a shower glass in the electromagnetic spectrum, significantly impairing the coherence of waves from underlying acoustic anomalies. Helioseismic diagnostics based on a clear understanding of the acoustics of strong magnetic fields offer the possibility of a practical general model of the "acoustic showerglass" in terms of thermal structure and flows in the upper active region subphotosphere. Such a model could serve as the basis for a magnetic proxy that would facilitate an optical correction of the acoustic showerglass, significantly restoring the coherence of seismic images focused on thermal anomalies and flows 10--20 Mm beneath the photosphere. We are convinced that detailed hydromagnetic computations of subphotospheric acoustics are a major key to the control work needed for a realistic understanding of the structure and dynamics of active region subphotospheres.