**AAS Meeting #194 - Chicago, Illinois, May/June 1999**

*Session 21. Solar Interior*

Oral, Monday, May 31, 1999, 10:00-11:30am, Continental Ballroom A
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## [21.03] The Effects of Large-Scale Convective Structures on Solar Eigenfrequencies

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

Although the differences between observed p-mode
eigenfrequencies and those calculated from solar models are
small, they are significant. Strong evidence supports the
contention that convection is responsible for much of the
discrepancy. In most solar models, mixing-length
parameterizations are used only to establish the mean
structure of the convection zone; however, no efforts are
made to calculate the influence of convective structures on
p-mode eigenfrequencies.

I will review an algorithm we have developed, using a method
known as adiabatic switching, which allows us to determine
the eigenfrequencies of p-modes in complex convective
structures. This method is valid when describing p-modes in
the ray approximation (not as global modes of oscillation).
This requirement is equivalent to the familiar WKB
approximation and restricts our considerations to
large-scale convective motions. Our current work focuses on
two-dimensional plane-parallel convection which includes
variations in the local sound speed (temperature) as well as
advective motions of the underlying fluid.

I will present results from several convective simulations:
Rayleigh-Bénard cells, thermal plumes (such as are found
on supergranular boundaries), and turbulent convective
models. Our investigations show that simple models of
convective cells produce downshifts which are second-order
in the strength of the perturbation. More complex
simulations, while consistently displaying downshifts,
exhibit more complicated dependences on the strength of the
convection. Finally, we demonstrate the dependence of the
shift on the radial order n and degree l of the modes
and show they agree with analytic estimates. At the minimum,
these results demonstrate convective effects are of the
proper sign and magnitude to explain the observed
discrepancies although a complete correspondence with data
has not yet been established.

If the author provided an email address or URL for general inquiries, it is a
s follows:

swisdak@ucsub.colorado.edu

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