Torsional oscillations in the solar convection zone

Recent analysis of the helioseismic observations indicate that the previous ly observed surface torsional oscillations extend significantly downwards i nto the solar convection zone. In an attempt to understand these oscillations, we study the nonlinear coup ling between the magnetic field and the solar differential rotation in the context of a mean field dynamo model, in which the nonlinearity is due to t he action of the azimuthal component of the Lorentz force of the dynamo gen erated magnetic field on the solar angular velocity. The underlying zero or der angular velocity is Chosen to be consistent with the most recent helios eismic data. The model produces butterfly diagrams which are in qualitative agreement wi th the observations. It displays torsional oscillations that penetrate into the convection zone, and which with time migrate towards the equator. The period of these oscillations is found to be half that of the period of the global magnetic fields. This is compatible with the observed period of the surface torsional oscillations. Inside the convection zone, this is a testa ble prediction that is not ruled out by the observations so far available.