Implementation of an atmosphere-ocean general circulation model on the expanded spherical cube

A hydrodynamical kernel that drives both an atmospheric and oceanic general circulation model is implemented in general orthogonal curvilinear coordinates using the finite-volume method on the sphere. The finite-volume method naturally describes arbitrary grids, and use of the vector-invariant form of the momentum equations simplifies the generalization to arbitrary coordinates. Grids based on the expanded spherical cube of Rancic et al., which contain eight singular points, are used. At these singularities the grid is nonorthogonal. The combined use of vector-invariant equations and the finite-volume method is shown to avoid degeneracy at these singular points. The model is tested using experiments proposed by Williamson et al. and Held and Saurez. The atmospheric solutions are examined seeking evidence of the underlying grid in solutions and eddy statistics. A global ocean simulation is also conducted using the same code. The solutions prove to be accurate and free of artifacts arising from the cubic grid.