Transport by mean flows in stellar radiative zones

The penetration of meridional flows below the base of the convection zone of solar-type stars may play a significant role in the transport of chemical species, angular momentum and magnetic fields within their stable radiative zones. We systematically study these large-scale flows by performing a series of three-dimensional numerical simulations in a rotating spherical shell that consists of an outer convective region that lies on top of a stable zone. We vary the number of density scale heights in the convection zone, the degree of convective driving and the rotation rate, and investigate the dynamical balances and angular momentum transport established throughout the convection zone and the radiative interior within different parameter regimes. When operating in the solar-like regime, where the Eddington–Sweet timescale t_ES is shorter than the viscous timescale t_ν, as measured by the parameter σ = (t_ES/t_ν)^0.5, we find that the mean flows can propagate large distances beyond the inner convective boundary into the radiative interior. We present scaling laws of the penetration depth of these mean flows below the base of the convection zone with respect to σ. Our findings may shed new light on the role that the meridional flows play in different dynamical processes occurring within stellar interiors.