Excitement of the Toroidal Field in Mantle Convection

Abstract

In this paper we discuss the excitement of toroidal field in mantle convection by the viscosity within the mantle and the boundary conditions applied to the earth’s surface and the CMB. Our analyses show that in the mantle with homogeneous viscosity the toroidal field decouples from the poloidal field and doesn’t affect the gravitational potential; While in the mantle with inhomogenous viscosity the toroidal field and the poloidal field couple together and both affect the gravitational potential. When the plate velocities are introduced, the boundary condition becomes nonzero, this nonzero boundary condition can excite toroidal field also in a homogeneous mantle, but the zero boundary condition can’t.