  Mean-field hydrodynamics advanced to clear explanations for the origin and
properties of the global meridional flow in stellar convection zones.
Qualitative arguments and analysis of basic equations both show that the
meridional circulation is driven by non-conservative centrifugal and buoyancy
forces and results from a slight disbalance between these two drivers. The
deviations from the thermal wind balance are relatively large near the
boundaries of convection zones. Accordingly, the meridional flow attains its
largest velocities in the boundary layers and decreases inside the convection
zone. This picture, however, is neither supported nor dismissed by the
conflicting results of recent helioseismic soundings or 3D numerical
experiments. The relevant physics of the differential temperature and its
possible relation to the solar oblateness are briefly discussed.
