Effect of horizontal turbulent diffusion on transport by meridional circulation.

The effect of horizontal turbulent motions on the transport of chemicals by meridional circulation in a stellar radiation zone ar examined. It is shown that strong enough turbulent diffusion inhibits the advection of a chemical element, because it tends to homogenize horizontal layers. The vertical transport then reduces to a diffusion process, a phenomenon similar to the classical shear dispersion in a pipe flow. Likewise, the differential rotation is presumably smoothed out in latitude, but this will not greatly hinder the advection of angular momentum