P24 - Geodynamo Simulations in a Full Sphere
DescriptionAlthough the geomagnetic field exists since about 4 Gyr, recent estimates for the formation of the Earth's inner core go back no further than 500 Myr to 1 Gyr. Here we run rapidly rotating dynamos in a full sphere geometry, representative of the Earth's dynamo before the nucleation of the inner core. Numerically, the full sphere bears the difficulty of an adequate treatment of the singularity at the center. We perform a set of numerical simulations using a fully spectral simulation framework, where a careful choice of the radial basis functions resolves this singularity and allows us to systematically study the influence of three non-dimensional parameters, namely the Ekman number E (measuring viscous to Coriolis force), the Rayleigh number Ra (measuring the convective forcing) and the magnetic Prandtl number Pm (ratio of viscous and magnetic diffusivity). The output of our simulations allows us to characterize the dynamo regime as a function of Ra and Rm, which differs from similar diagrams for spherical shell geometry. In particular, we find that the regime of dipolar magnetic fields is narrower in the full sphere and a larger Pm is needed for dynamo action. Finally, we derive scaling laws for input and output parameters.
TimeMonday, June 2611:20 - 11:50 CEST