  A new kind of overset grid, named Yin-Yang grid, for spherical geometry is
proposed. The Yin-Yang grid is composed of two identical component grids that
are combined in a complemental way to cover a spherical surface with partial
overlap on their boundaries. Each component grid is a low latitude part of the
latitude-longitude grid. Therefore the grid spacing is quasi-uniform and the
metric tensors are simple and analytically known. One can directly apply
mathematical and numerical resources that have been written in the spherical
polar coordinates or latitude-longitude grid. The complemental combination of
the two identical component grids enables us to make efficient and concise
programs. Simulation codes for geodynamo and mantle convection simulations
using finite difference scheme based on the Yin-Yang grid are developed and
tested. The Yin-Yang grid is suitable for massively parallel computers.

Geophysics;Computational Physics