Theory of differential rotation and meridional circulation

Kitchatinov Leonid, kit@iszf.irk.ru, Institute for Solar-Terrestrial Physics, Irkutsk, Russia

Abstract
Differential rotation and meridional flow in the stellar convection zones are mutually related. Meridional flow results from slight deviation from thermal wind balance, which balance depends on differential rotation. The flow in turn changes the angular velocity distribution to bring it closer to the thermal wind balance. Mean-field hydrodynamics explains the differential rotation by interaction between stellar turbulent convection and rotation. Numerical model based on this theory reproduces observations of solar differential rotation and meridional flow quite closely. Application of the model to individual solar-type stars also agree with observations. Functional dependence of the surface differential rotation on rotation rate and surface temperature is predicted. The differential rotation varies slightly with rotation period but increases sharply with temperature. The efficiency of differential rotation in generating magnetic fields estimated in terms of the standard C_\Omega parameter of dynamo models has an opposite trend: strong differential rotation of F-stars is found to be less dynamo-efficient than weak rotational shear of M-stars. Variation of the amplitude and structure of meridional flow with stellar mass and rotation rate is discussed.