A Model of P-mode Scattering by Sunspots
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**Session 44 -- Solar Observations and Theory**
*Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm*

## [44.06] A Model of P-mode Scattering by Sunspots

*Y. Fan (NSO), D.C. Braun ( Sol. Phys. Res. Corp.)*

It has recently been discovered that sunspots scatter
intermediate and high-degree p-modes. The scattering may
be characterized by a shift in phase between modes travelling
toward and away from the spot. These observations offer the hope
that suitable models of the scattering may yield important clues about the
subsurface evolution and structure of magnetic regions.

We model the scattering of p-mode waves in a polytropic atmosphere
by localized inhomogeneities in compressibility
(the wave speed), density and pressure of the media.
The effect of the inhomogeneities is to introduce a source term
in the pressure wave equation.
We solve this inhomogeneous equation for the scattered wave
amplitudes using standard Green's function techniques under the
simplification of the Born approximation.
We found that with reasonable strength (or contrast) of the imhomogeneities
we can obtain phase shifts between the outgoing and the in-going waves
similar to observations of p-modes in both the magnitude
and degree ($\ell$) dependence.
We discuss how the strength of the scattered waves may depend on the
depth distribution of the inhomogeneities.

This work is supported by a NSF grant AST-9496171 and NASA grant
NAGW-4143 awarded to DCB. YF is supported by ONR grant N00014-91-J-1040.

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