Meridional motion and the slope of isorotation contours

As helioseismic inversions have continued to improve in precision, it has become apparent that in the bulk of the solar convection zone the contours of rotation, while certainly not parallel to the rotation axis as predicted in earlier global convection simulations, are also not radial, as has often been stated based on earlier inversions. Instead, between 15 and about 55 degrees latitude (measured at r = 0.8R) the rotation contours make an angle with the rotation axis of about 25 degrees, which does not appear to vary systematically with latitude in this latitude range. What then determines this angle? By use of an extremely simple dynamical equilibrium model, we show that coriolis forces from the observed meridional circulation could be responsible for this angle if, without this effect, the contours of rotation would be radial.