Implementation of the Fourier Transform Method for Geodynamo Simulation on the Earth Simulator

Most of the computer codes for the recent simulation studies of geodynamo are based on a spectral transform method in which variables are expanded in spherical harmonics. This method, however, is not suitable for high-resolution simulations because of a large amount of computation for spectral transform with respect to Legendre functions. In this study, we developed a modified code based on the Fourier transform method in which the Legendre transform is avoided and the remaining two-dimensional differential equations in the meridional plane are solved by finite differences. The details of the implementation technique of the Fourier transform method on the Earth Simulator are described. The performance tests of the developed code are also reported.