Fluid motions induced by horizontally heterogeneous Joule heating in the Earth’s inner core

Abstract

Horizontally heterogeneous Joule heating is proposed as a new driving source for fluid motions in the Earth’s inner core. The magnetic field imposed at the inner core boundary (ICB) penetrates into the inner core through diffusion and generates Joule heating. When the heating distribution is horizontally heterogeneous, it produces torque by means of the buoyancy force, thereby inducing fluid motions in the inner core. The expression of fluid flows induced by arbitrary magnetic field distributions at ICB is obtained analytically. Using the estimated values of the physical parameters of the inner core, the amplitude of the stress field associated with the flows induced by this mechanism is expected to be greater than or approximately the same as that of the models considered thus far, and is sufficiently large for large scale deformation of the inner core. The flow field by this mechanism is also accompanied by a weak stress field layer near the ICB. The thickness of this boundary layer is comparable to the depth of the weak anisotropy region observed near the ICB. The model presented herein suggests that interactions of the flow and magnetic fields through Joule heating may occur between the inner and outer cores. The flow field induced by Joule heating generates mass exchange through the ICB, causing absorption and release of latent heat and light elements. This process affects the flow field and the dynamo action in the outer core and possibly reflects on the distribution of the magnetic field. The variation of the magnetic field penetrates the ICB again and modifies the distribution of Joule heating and the resultant flow field in the inner core.