On the MHD structure of the solar tachocline. Steady and dynamical solutions

Details On the MHD structure of the solar tachocline. Steady and dynamical solutions On the MHD structure of the solar tachocline. Steady and dynamical solutions

Dec 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998newa....3..671h&link_type=abstract

New Astronomy, vol. 3, no. 8, p. 671-685.

Astronomy and Astrophysics

Astronomy

3

Mhd, Turbulence, Sun: Rotation, Sun: Magnetic Fields, Sun: Interior, Methods: Numerical

Scientific paper

Using recent helioseismology measurements, we carry out a parameter study to investigate the steady and unsteady configurations of the solar tachocline (hereafter ST) between the differentially rotating convection zone and the underlying solid-body rotating core. It is shown that in the case of steady solutions, a poloidal magnetic field of quadrupole type topology generates toroidal flux tubes (hereafter B_T) that are three times stronger than in the dipole case. In both cases however, B_T acquires values that are far below those required to overcome distortion via convective turbulence. These values remain rather sensitive to the conditions imposed on the boundaries and on the underlying viscosity prescription. They appear however to have a weak dependence on the width of the ST. For example, imposing a 50 G poloidal field or stronger on the outer boundary yields unsteady solutions only. Using the above-obtained steady configurations as initial conditions, we carried out several calculations to follow the evolution of the flow over several hundred dynamical time scales. It appears that the final dynamical solutions obtained differ significantly from their corresponding initial profiles. Moreover, a large scale polewards oriented motion always results independent of whether magnetic effects are in- or excluded. The numerical results indicate that the ST is likely to be governed by purely hydrodynamical or weakly magnetized flows in order to re-produce Omega-profiles that are consistent with the helioseismology measurements. The storage of a strong B_T in the near-equator region as a possible scenario for the evolution of the sun spots is numerically investigated as well.

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