Sunspot rotation rates along the butterfly diagram

Sunspots in the left part of the butterfly diagram tend to have greater angular velocity than those in the right. If we assume that toroidal magnetic fields are younger in the left part of the diagram than in the right, we deduce that sunspots associated with younger toroidal magnetic fields tend to have greater angular velocity than those associated with older magnetic fields. The result could at least be associated to the Howard and LaBonte torsional oscillations of the unmagnetized plasma: an appropriate analysis shows that this effect also seems to be present.