Origin of the Near-Surface Shear Layer of Solar Rotation

Helioseismology has revealed an increase in the rotation rate with depth in a thin ($\sim$30 Mm) near-surface layer. The normalized rotational shear in this layer is independent of latitude. This rotational state is shown to be a consequence of the short characteristic time of near-surface convection compared to the rotation period, and the radial anisotropy of the convective turbulence. Analytical derivations within mean-field hydrodynamics reproduce the observed normalized rotational shear and are in agreement with numerical experiments on the radiative hydrodynamics of solar convection. The near-surface shear layer is the source of the global meridional flow important for the solar dynamo.