Latitude-Longitude Grid Suitable for Numerical Time Integration of a Global Atmospheric Model

Abstract

A simple, free-surface, barotropic model and a nine-level, baroclinic model are numerically time integrated on both latitude-longitude grids and on Kurihara-type grids to compare the results obtained from the two grid systems. The prognostic variables are Fourier space-filtered in the longitudinal direction on the latitude-longitude grids to permit the use of the same time-step length on both grids. With respect to geopotential height and zonal wind distributions and to the phase speed of wave propagation, the results from the barotropic model, time-integrated on a sector latitude-longitude grid, agree better with a high-resolution control run than those computed on a modified Kurihara grid, particularly at high latitudes. The barotropic model is also time-integrated on a hemispheric, latitude-longitude grid, and the results compare well with a high-resolution control. The latter comparison is performed on initial data having strong cross-polar flow. The mean sea-level pressure distribution obtained from a 64-day time integration of the baroclinic model on a global, latitude-longitude grid is better than that derived from a similar model using a Kurihara grid of comparable resolution. For example, the tendency for the Kurihara grid model to predict excessive pressures in the north polar region is for the most part corrected by use of the latitude-longitude grid.