Numerical Modeling of the Absorption and Scattering of Acoustic Radiation by Sunspots

Authors:
Open Access
Publisher website
Google Scholar
Abstract
We present numerical calculations of the scattering of acoustic-gravity waves by a model sunspot consisting of an inhomogeneous, vertically magnetized region embedded in a polytropically stratiÐed layer. The calculations show the transformation of incoming f-mode and p-mode power into downwardpropagating, slow magnetoacoustic waves resulting in substantial absorption of incident f-modes and Ðrst-order p-modes and indicating that the slow-mode transformation model is a viable explanation for the observed absorption. In addition to absorption, we Ðnd large scattering phase shifts for the f-modes. Phase shifts are small for all p-modes. Coupling between modes of di †erent radial order is generally small. The remaining di †erences between our results and the observations may constitute evidence that, if the mode transformation picture is correct, real sunspots must deviate signiÐcantly from the simple unidirectional Ðeld geometry we use here. In particular, we suggest that a sunspot consisting of a bundle of Ðbrils, in each of which the magnetic Ñux density increases rapidly with depth, would reproduce more closely the measured strong absorption and scattering of p-modes.

This publication has 23 references indexed in Scilit: