SOLAR TORSIONAL OSCILLATIONS DUE TO THE MAGNETIC QUENCHING OF THE REYNOLDS STRESS

The solar torsional oscillations are considered as the response of the Reynolds stress to the time-dependent dynamo-induced magnetic field. This picture is opposite to the so far accepted idea that it is the la rge-scale Lorentz force which directly drives the temporal variations of the surface rotation profile. Here, the ''magnetic quenching'' of t he components of the Reynolds stress - viscosity tensor and Lambda-eff ect - is the basic reason for the cyclic rotation law. In order to pro duce the suppressing magnetic field it was necessary to construct a tu rbulent dynamo. Its site is the overshoot region, with the alpha-effec t existing only in an equatorial domain. The produced butterfly diagra m is shown in Fig. 5. Mainly the toroidal field quenches the turbulent Reynolds stress deep in the convection zone. For a simplified model w e find indeed that an observable flow pattern of 1-2 m/s appears with the correct frequency at the solar surface. The pattern can be interpr eted as a wave originating at 30 degrees and vanishing at the equator. The phase relation with respect to the magnetic field does, however, not meet the observations. A more complete model of the solar overshoo t dynamo works with turbulence intensities of 20 m/s and turnover time s from mixing length theory. The complete Reynolds tensor is applied. The magnetic diffusivity below the overshoot domain is put to 10(10) C m-2/s. Then the surface value of the 'torsional oscillation' increases to values up to 3 m/s and the phase relation between magnetic cycle a nd torsional oscillations is correct. The amplitude of the oscillation s proves to depend strongly on the magnetic Prandtl number. The result s indicate that the value of the turbulent viscosity should not be sma ller than 10(10) cm(2)/s.