A three-dimensional multilayered spherical dynamic interface dynamo using the malkus-proctor formulation

Abstract

We investigate a fully three-dimensional and multilayered spherical dynamic interface dynamo using a finite-element method based on the three-dimensional tetrahedralization of the whole spherical system. The dynamic interface dynamo model consists of four magnetically coupled zones: an electrically conducting and uniformly rotating core, a thin differentially rotating tachocline, a turbulent convection envelope, and a nearly insulating exterior. In the thin tachocline at the base of the convection zone, a differential rotation, similar to that of the observed solar differential rotation, is imposed. In the convection zone, the Malkus-Proctor formulation with a prescribed α-effect is employed while the fully three-dimensional dynamic feedback of Lorentz forces is taken into account. Our numerical simulations of the dynamic interface dynamo are focused on the Taylor number Ta = 105 with a unity magnetic Prandtl number. It is shown that the dynamic interface dynamo, depending on the size of the magnetic Reynolds number Rem based on the differential rotation, can be either nonaxisymmetric or axisymmetric. When Rem is small or moderate, the dynamic dynamo is characterized by quasi-periodic and nonaxisymmetric azimuthally traveling waves. When Re m is sufficiently large, the dynamo is characterized by a strong toroidal magnetic field, axisymmetric or nearly axisymmetric, that selects dipolar symmetry and propagates equatorward. Implications of our dynamic interface dynamo for the solar dynamo are also discussed. © 2008. The American Astronomical Society. All rights reserved.