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Nonlinear Anelastic Modal Theory for Solar Convection*

Published online by Cambridge University Press:  12 April 2016

Jean Latour ,
Juri Toomre  and
Jean-Paul Zahn
Jean Latour
Affiliation:
Joint Institute for Laboratory Astrophysics**, University of Colora, and Observatoire de Nice, BP252, F06007 Nice CEDEX, France‡
Juri Toomre
Affiliation:
Department of Astrophysical, Planetary and Atmospheric Sciences†, and Joint Institute for Laboratory Astrophysics**, University of Colorado, Boulder, CO 80309, U.S.A.
Jean-Paul Zahn
Affiliation:
Observatoire du Pic-du-Midi et de Toulous, F65200 Bagnères de Bigorre, France

Abstract

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Preliminary solar envelope models have been computed using the single-mode anelastic equations as a description of turbulent convection. This approach provides estimates for the variation with depth of the largest convective cellular flows, akin to giant cells, with horizontal sizes comparable to the total depth of the convection zone. These modal nonlinear treatments are capable of describing compressible motions occurring over many density scale heights. Single-mode anelastic solutions have been constructed for a solar envelope whose mean stratification is nearly adiabatic over most of its vertical extent because of the enthalpy (or convective) flux explicitly carried by the big cell; a sub-grid scale representation of turbulent heat transport is incorporated into the treatment near the surface. The single-mode equations admit two solutions for the same horizontal wavelength, and these are distinguished by the sense of the vertical velocity at the center of the three-dimensional cell. It is striking that the upward directed flows experience large pressure effects when they penetrate into regions where the vertical scale height has become small compared to their horizontal scale. The fluctuating pressure can modify the density fluctuations so that the sense of the buoyancy force is changed, with buoyancy braking actually achieved near the top of the convection zone. The pressure and buoyancy work in the shallow but unstable H+ and He+ ionization regions can serve to decelerate the vertical motions and deflect them laterally, leading to strong horizontal shearing motions. It appears that such dynamical processes may explain why the amplitudes of flows related to the largest scales of convection are so feeble in the solar atmosphere.

Type
Research Article
Information
International Astronomical Union Colloquium , Volume 66: Problems of Solar and Stellar Oscillations , 1983 , pp. 387 - 400
Copyright
Copyright © Reidel 1983

Footnotes

**

JILA is operated jointly by the University of Colorado and the National Bureau of Standards.

†

Formerly Department of Astro-Geophysics.

‡

Now at Observatoire du Pic-du-Midi et de Toulouse.

*

Proceedings of the 66th IAU Colloquium: Problems in Solar and Stellar Oscillations, held at the Crimean Astrophysical Observatory, U.S.S.R., 1–5 September, 1981.

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