34th Solar Physics Division Meeting, June 2003
Session 26 The Changing Solar interior II
Oral, Friday, June 20, 2003, 9:00am-12:00noon, Auditorium

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[26.07] Convective Overshoot at the Base of the Solar Convection Zone - a Semi-Analytical Approach

M. Rempel (HAO/NCAR)

Despite the importance of overshoot at the base of the solar convection zone for the storage of strong toroidal magnetic field produced there by the solar dynamo, the uncertainties concerning the depth and mean subadiabatic stratification are large. Overshoot models of the past, based on the non local mixing-length theory, generally produce a shallow weakly subadiabatic region with a sharp transition to the radiative interior, whereas several numerical simulations lead to significantly subadiabatic overshoot with penetration depth of more than a pressure scale height. I present a semi-analytical convection zone/overshoot model based on the assumption that the convective energy flux is governed by downflow structures with a low filling factor, which allows for modeling both, the parameter regime addressed by non-local mixing-length approach as well as the regime addressed by numerical simulations. It turns out that the main discrepancies between the non-local mixing-length approach and numerical simulations are due to the much larger energy flux used in numerical simulations. Furthermore this model shows that the sharp transition between the nearly adiabatic overshoot and radiative interior, a typical result of the non-local mixing-length approach which is in contradiction with helioseismology, can be avoided by assuming an ensemble of downflows with different strength (Mach number).

NCAR is sponsored by the National Science Foundation.

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.