Streamlines of the meridional circulation for the inviscid solution with E → 0 (left) and for the full problem (E = 10^-7) including the viscous force (right). Solid lines and dashed lines represent counter-clockwise and clockwise circulation, respectively. In the viscous solution, the streamlines are closed inside the boundary layer. For these calculations, one solar mass of ideal gas with Kramers’ opacities was enclosed in a bounding sphere at the pole of which the pressure is 10^-4 times the central value (see Espinosa Lara & Rieutord 2007, for a description of this model).