Differential rotation of a star induced by meridional circulation

Abstract

Global meridional flows in stars transport angular momentum, thus giving rise to nonuniform rotation. The pattern of differential rotation associated with slow meridional circulation depends on the direction of this circulation. A flow directed from the poles to the equator at the surface and from the equator to the poles in deep layers results in relatively fast rotation of the equatorial zone. If the circulation is directed oppositely, the angular velocity increases from the equator to the poles. Relatively fast rotation at the poles may also result from fast circulation, irrespective of its direction. A simple illustrative explanation is given here to these results. Analytical estimates are supported by numerical calculations. The time variations in the meridional flow observed on the Sun should contribute to torsional oscillations.