  The propagation of meridional circulation below the base of the convection
zone of low-mass stars may play a crucial role in the transport of angular
momentum and also significantly contribute to the transport of chemical species
and magnetic fields within their stable radiative zone. We systematically study
these large-scale mean flows by performing three-dimensional (3D) global
numerical simulations in a spherical shell that consists of a convection zone
(CZ) overlying a stably stratified region. We find that the meridional flows
can penetrate distances as large as $\sim 0.21r_o$ (where $r_o$ is the outer
radius) below the base of the convection zone, provided that the
Eddington-Sweet timescale $t_{ES}$ is much shorter than the viscous timescale
$t_{\nu}$ as measured by the parameter $\sigma=(t_{ES}/t_{\nu})^{1/2}$. In the
solar-like regime where $\sigma\lesssim 1$ in the upper radiative zone (RZ), we
find that the angular momentum transport in the deep RZ is determined primarily
by the action of the Coriolis force on meridional flows. In contrast, in models
run in the $\sigma> 1$ regime, the meridional flows become weaker and the
viscous effects dominate. We find that the penetration lengthscale
$\delta_{MC}$ of these mean flows when $\sigma\lesssim 1$ is proportional to
$\sigma^{-0.22}$. Our findings may provide a better understanding of the role
of the meridional flows in the dynamics of the solar interior and inform future
numerical studies that are focused on capturing solar-like dynamics
self-consistently.
