Large-scale Model of the Axisymmetric Dynamo with Feedback Effects

Abstract

A dynamo model is presented, based on a previously introduced kinematic model, in which the reaction of the magnetic field on the mass flow through the Lorentz force is included. Given the base mass flow corresponding to the case with no magnetic field, and assuming that the modification of this flow due to the Lorentz force can be treated as a perturbation, a complete model of the large-scale magnetic field dynamics can be obtained. The input needed consists in the large-scale meridional and zonal flows, the small-scale magnetic diffusivity, and a constant parameter entering the expression of the $\alpha$-effect. When applied to a solar-like star, the model shows a realistic dynamics of the magnetic field, including cycle duration, consistent field amplitudes with the correct parity, progression of the zonal magnetic field towards the equator, and motion toward the poles of the radial field at high latitudes. Also, the radial and zonal components show a correct phase relation, and, at the surface level, the magnetic helicity is predominantly negative in the northern hemisphere and positive in the southern hemisphere.