An anelastic evolutionary geodynamo simulation driven by compositional and thermal convection

Abstract

We have extended our geodynamo simulation 40 000 years using a more realistic representation of the thermodynamics and convection. The anelastic approximation replaces the Boussinesq approximation; and compositional buoyancy, in addition to thermal buoyancy, drives convection in the fluid outer core. Boundary conditions at the inner core boundary model the freezing of the heavy constituent onto the solid inner core and the release of the light constituent into the fluid outer core. The resulting simulated magnetic field has a strongly dipole dominated structure outside the core, similar to the Earth's field, so far displaying no tendency to reverse its dipole polarity. The non-dipolar structure of the field at the core-mantle boundary is also quite similar to the Earth's,including the rate of its general westward drift. As in our original simulation, the solid inner core typically rotates about 1°/yr faster than the mantle, in agreement with recent seismic studies of the Earth. This three-dimensional self-consistent solution seems to be simulating the stable regime of the geodynamo between reversals.