Hiroaki Matsui, University of Chicago

The fluid motion and the magnetic field in the Earth's outer core have small
scale components which cannot be resolved in numerical simulations because of
the small Ekman number and large Rayleigh number. Many geodynamo simulations
have been performed with much larger viscosity or hyper diffusivity, but more
realistic sub-grid scale (SGS) modeling is required. We model the influence of
sub-grid scale motion using the nonlinear gradient model by Leonard (1974).
This method is implemented in a dynamo simulation code the finite-element
method. To investigate basic behavior of the SGS terms, we compare the SGS
terms in the present model with the results obtained from a fully resolved
simulation on a finer grid.