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Effects of rotation and input energy flux on convective overshooting

Published online by Cambridge University Press:  01 August 2006

Petri J. Käpylä ,
M. J. Korpi ,
M. Stix  and
I. Tuominen
Petri J. Käpylä
Affiliation:
Observatory, P.O. Box 14, FI-00014University of Helsinki, Finland Kiepenheuer-Institut für Sonnenphysik, Schöneckstrasse 6, D-79104 Freiburg, Germany email: [email protected]
M. J. Korpi
Affiliation:
Observatory, P.O. Box 14, FI-00014University of Helsinki, Finland
M. Stix
Affiliation:
Kiepenheuer-Institut für Sonnenphysik, Schöneckstrasse 6, D-79104 Freiburg, Germany email: [email protected]
I. Tuominen
Affiliation:
Observatory, P.O. Box 14, FI-00014University of Helsinki, Finland
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Abstract

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We study convective overshooting by means of local 3D convection calculations. Using a mixing length model of the solar convection zone (CZ) as a guide, we determine the Coriolis number (Co), which is the inverse of the Rossby number, to be of the order of ten or larger at the base of the solar CZ. Therefore we perform convection calculations in the range Co = 0. . .10 and interpret the value of Co realised in the calculation to represent a depth in the solar CZ. In order to study the dependence on rotation, we compute the mixing length parameters αT and αu relating the temperature and velocity fluctuations, respectively, to the mean thermal stratification. We find that the mixing length parameters for the rapid rotation case, corresponding to the base of the solar CZ, are 3-5 times smaller than in the nonrotating case. Introducing such depth-dependent α into a solar structure model employing a non-local mixing length formalism results in overshooting which is approximately proportional to α at the base of the CZ. Although overshooting is reduced due to the reduced α, a discrepancy with helioseismology remains due to the steep transition to the radiative temperature gradient.

In comparison to the mixing length models the transition at the base of the CZ is much gentler in the 3D models. It was suggested recently (Rempel 2004) that this discrepancy is due to the significantly larger (up to seven orders of magnitude) input energy flux in the 3D models in comparison to the Sun and solar models, and that the 3D calculations should be able to approach the mixing length regime if the input energy flux is decreased by a moderate amount. We present results from local convection calculations which support this conjecture.

Keywords

ConvectionhydrodynamicsSun: interiorSun: helioseismologySun: rotation
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S239: Convection in Astrophysics , August 2006 , pp. 437 - 442
Copyright
Copyright © International Astronomical Union 2007

References

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