A COMPARISON OF SPHERICAL GRIDS FOR NUMERICAL INTEGRATION OF ATMOSPHERIC MODELS

The properties of spherical grids are reviewed and compared with one another. A quasi-homogeneous spherical geodesic grid is introduced to eliminate many of the undesirable features of other grids. The spherical geodesic grid is first compared with the other grids for integrating the nondivergent barotropic vorticity equation. Initial conditions are used for which an analytic solution exists. The spher-ical geodesic grid produces the best solution. The only observable error in the contoured output is a small phase error. Methods of developing difference approximations for the primitive barotropic modcl over triangular grids are first considered in cartesian geometry. Comparative integrations show that the six-point differences assoctated with triangular grids produce better solutions than square differences with similar resolution and the same order of triin-ation error