**AAS Meeting #193 - Austin, Texas, January 1999**

*Session 100. The Quiet and Active Sun*

Display, Saturday, January 9, 1999, 9:20am-4:00pm, Exhibit Hall 1
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## [100.03] The Effects of Convective Structures on p Mode Frequencies

*M. Swisdak, E. G. Zweibel (U. Colorado)*

While the correspondence between observed and predicted
p-mode frequencies is good, it is clear that the detailed
effects of convection are not adequately treated by
contemporary solar models. Even models of simple convective
structures which ignore the difficulties inherent in
realistically modelling solar convection encounter
difficulties in determining their effects on global
oscillations. However, under the WKB approximation p modes
may be treated as rays and their propagation described using
the formalism of Hamiltonian systems. This is an adequate
approximation for large-scale convection and modes of large
spherical harmonic degree \ell.

Only simple stellar models (polytropes, for example) have
eigenfrequencies which may be found analytically. However, a
computer program we have written using a method known as
adiabatic switching allows us to determine the
eigenfrequencies of modes in the ray approximation. The
motion of a ray is governed by a dispersion relation which
may account for several effects, including variations in the
local sound speed as well as advective motions of the
underlying fluid.

Our investigations have shown that simple models of
convective cells produce downshifts in the eigenfrequencies
which are of second-order in the strength of the
perturbation. At the minimum, this result is of the proper
sign to explain the observed discrepancy although it is
unclear if the correction is large enough to account for the
entire effect.

In addition, we demonstrate the dependence of the shift on
the radial order n and degree \ell of the mode and show
that they roughly agree with our analytic estimates
predicting a frequency shift which varies as a/\ell +
b\ell where a and b are constants. Finally, we consider
the case of a ray interacting with a thermal plume such as
those observed at the edges of granules and supergranules.

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

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