On the nature of the core-envelope boundary layer in a slowly rotating star

In this paper we discuss the large-scale meridional currents and differential rotation in the radiative envelope of a single, nonmagnetic, early-type star. Our solutions depend on the interaction between these large-scale motions and the small-scale baroclinic eddies, which are an ever-present feature of a stellar radiative zone. If one makes allowance for mean steady motions in a typical rotating star, then large eddy viscosities are necessary for the method to converge. We show that there exists a singular, thermo-viscous boundary layer at the interface between the convective core and the radiative envelope. Unless very unrealistic assumptions are made, this layer is not of the Ekman type.