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**Session 74 - The Quiet & Active Sun.**

*Display session, Friday, January 09*

*Exhibit Hall, *

## [74.02] Probing Convective Effects on p modes using the Adiabatic Switching Method

*M. Swisdak, E. Zweibel (U. Colorado, JILA)*
While the correspondence between observed and predicted
p-mode frequencies is generally good, it is clear that the
detailed effects of the convection zone are not adequately treated
by contemporary solar models. Indeed, this discrepancy is to be expected
since the effects of simple convective structures on p-mode frequencies and
linewidths are not completely understood. While the full problem is
difficult to treat, under the WKB approximation p modes may be treated as
rays and their propagation can be described using the formalism of
Hamiltonian systems.

In general, only simple stellar models such as polytropes have
analytic solutions for the eigenfrequencies. However, I have written
computer code which uses the method of adiabatic switching (Skodje amp;
Cary, 1988) to determine the
approximate eigenfrequencies of a ray with a given dispersion relation
traveling through a medium with prescribed variations in the local wave
velocity.

In this application of the method of adiabatic switching, the initial
state is a ray propagating in a polytropic spherical
shell. Variations in the properties of the medium (e.g., sound
speed perturbations or advective flows) are expressed as time-dependent
perturbations to the Hamiltonian. These perturbations are turned on
slowly and, consequently, the ray adiabatically adjusts its frequency,
eventually yielding the eigenfrequency for the final state.
The method is well-suited for describing the effects of time-dependent
convection.

This method gives accurate eigenfrequencies
for a number of trial simulations, including wave speed perturbations and
simple models of convective cells. By coupling
this program to snapshots of convective simulations,
I can determine both frequency shifts and line widths of p modes and compare
them to high-quality data sets such as those taken by the
MDI instrument on SOHO.

\bigskip

Skodje, R., amp; Cary, J. 1988, Comp. Phys. Reports, 8, 221.

The author(s) of this abstract have provided an email address for comments about the abstract: swisdak@solarz.colorado.edu

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