Non-kinematic flux-transport dynamos and torsional oscillations

We present a non-kinematic flux-transport dynamo model for the Sun that combines a meanfield model for differential rotation and meridional flow with the meanfield induction equation. The induced magnetic field is allowed to feed back on differential rotation and meridional flow through the macroscopic Lorentz force, leading to solar cycle variations of zonal and meridional flows. We show that the dynamo saturates through this feedback at a field strength of around 1 to 1.5 T and that the equatorward transport of field by the meridional flow at the base of the convection zone (essential for flux-transport dynamos) is not significantly reduced. The non-linear dynamo is capable of explaining the high latitude branch of torsional oscillations (with correct amplitude and phase relation with respect to the magnetic butterfly diagram), but cannot explain the low latitude branch through macroscopic Lorentz-force feedback. We present a compound model that includes a parameterization of enhanced radiative losses in the active region belt (following the idea of H.C. Spruit) and show that this can provide the correct oscillation pattern in low latitudes close to the surface. Thermally driven inflows into the active region belt produced by this model are also consistent with observations.