[S-EM34] Geomagnetism, paleomagnetism and rock magnetism

[SEM34-10] Thermal structure of the inner core boundary in numerical dynamos

*Hiroaki Matsui¹ (1.Dept. of Earth and Planetary Sciences, University of California, Davis)

Keywords:geodynamo simulations, Inner core boundary

Seismic anisotropy through alignment of crystal lattices suggests aspherical growth of the inner core. Slow viscous deformation of the inner core and latent heat distribution by flow motion are expected to be the origin of the aspherical growth of the inner core. A number of dynamo simulations has been performed with prescribed boundary conditions at ICB to take into account the inner core heterogeneity. In the present study, we perform geodynamo simulations with considering the heat equation in the inner core. To compare the results with the simulation without considering the inner core, we assume that the inner core is electrically insulated and co-rotate with mantle. In addition, we set the same thermal diffusivity for the inner core and outer core, and introduce a constant heat source in the inner core to keep the average temperature in the outer core through the simulations. We also set a homogeneous heat flux at the outer boundary of the shell as a thermal boundary condition at CMB. We compare the simulations results with the simulations results using fixed heat flux or temperature condition at ICB. The results show that the time averaged thermal structure at ICB is likely to the homogeneous heat flux boundary conditions. The time averaged lateral temperature variation is approximately 26% of the average temperature difference between ICB and CMB, while lateral heat flux variation is only 6% of the average heat flux at the ICB. We also observe small scale temperature and heat flux variations; however, these components vary with time. In addition, the length scale of the heat flux variation is smaller than the temperature variation at ICB.