Origin of the Near-Surface Rotational Shear Layer of the Sun

Abstract

Helioseismology has revealed an increase in the rotation rate with depth in a thin (∼30 Mm)near-surface layer. The normalized rotational shear in this layer does not depend on latitude. This rotationalstate is shown to be a consequence of the short characteristic time of near-surface convection comparedto the rotation period and radial anisotropy of convective turbulence. Analytical calculations within meanfieldhydrodynamics reproduce the observed normalized rotational shear and are consistent with numericalexperiments on radiative hydrodynamics of solar convection. The near-surface shear layer is the source ofglobal meridional flow important for the solar dynamo.