DIFFERENTIAL ROTATION IN SOLAR-TYPE STARS - REVISITING THE TAYLOR-NUMBER PUZZLE

Differential rotation and meridional circulation in a solar-type star are computed. Rotationally-induced anisotropy and quenching of the edd y diffusivities are included. The resulting iso-contours of the angula r velocity in the solar convection zone are close to the data of helio seismology. The anisotropy of the convective heat transport prevents t he realization of the expected Taylor-Proudman state. The anisotropy p roduces a latitudinal temperature variation with warm poles and cool e quator. The corresponding circulation opposes the meridional flow driv en by the centrifugal force hence the net flow is very dow. The model is also applied to the (old) slowly-rotating Sun. The rotation law exh ibits only a small latitudinal variation, its angular velocity decreas es inwards. This is similar to a model artificially ignoring the merid ional flow. The how, however, produces a strong effect for (young) fas t rotators decreasing their differential rotation. For sun-like stars, a decrease of the differential rotation with rotation rate is found. Also the model predictions for meridional circulation and differential rotation in a K5-star with deep convection zone are discussed.