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.

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