Development of Numerical Simulation of the Earth and Planetary Dynamos

In recent years, numerical simulation of the three-dimensional geodynamo has advanced considerably, and some fundamental properties of convection and magnetic field generation in the Earth's core have been understood. In this paper, we introduce the latest results of threedimensional geodynamo simulation, and show some bases of convection and magnetic field generation processes. With decrease in the Ekman number, the length scale of convection becomes much smaller, while the magnetic field tends to show large-scale structure as the dipole field. At a high Rayleigh number, polarity reversals of the dipole field occur irregularly. Furthermore, it turns out that the reversal frequency depends strongly on the Rayleigh number. Although nondimensional parameters used in simulations are still far from the real Earth, some characteristic features such as a power spectrum similar to the geodynamo are found in numerical dynamo models. Using numerical dynamo simulations, we would infer dynamics deep in planets.