LOCAL ACOUSTIC DIAGNOSTICS OF THE SOLAR INTERIOR

The observed absorption of p-modes by sunspots and solar magnetic fields has raised the possibility of developing holographic techniques to probe local magnetic features within the solar interior. Two simple diagnostic utilities are developed and tested to search for evidence of subsurface p-mode absorption. These consist of maps of acoustic power and maps of what we term the surface acoustic flux vector. Maps of acoustic power for a 50 hr sequence of solar Ca II K-line images show power deficits at 3 mHz corresponding to surface magnetic flux and power enhancements surounding active regions (halos) at 6 mHz. The general suppression of wave amplitude inside magnetic regions is due to the waves becoming less visible, and does not indicate wave absorption. The 6 mHz halos are observed to extend well beyond the active regions into quiet Sun and we believe it likely that they represent a true emission of waves. Faint 3 mHz power deficits are also seen, extending in long fingers from active regions far into areas of quiet-Sun. These fingers tend to cross the equator to connect active region bands. They also rotate with the Sun. We think they represent subsurface absorption of p-mode power. Acoustic power maps alone do not unambiguously determine the presence of absorbing or emitting regions. A vector quantity which we term the surface acoustic flux vector is used to circumvent this liability. This vector is defined as the time-average of the product of the spatial gradient and the time derivative of the wave amplitude. This flux vector is essentially a measure of the time-reversal variance of the wave motion and its divergence is an indicator of wave emission or absorption. Surface acoustic flux vector maps of two active regions were constructed for two 6 hr time-series of dopplergrams. Both maps clearly show the divergence of 3 mHz acoustic flux into surface magnetic structures and also sources and sinks of wave energy which are not associated with surface features.