Simulation of Climate by a Global General Circulation Model

The primitive equations of motion in spherical coordinates are integrated with respect to time on global grids with mean horizontal resolutions of 500 and 250 km. There are nine levels in the models from 80 m to 28 km above the ground. The models have realistic continents with smoothed topography and an ocean surface with February water temperatures prescribed. The insolation is for a Northern Hemisphere winter. I n addition to wind, temperature, pressure, and water vapor, the models simulate precipitation, evaporation, soil moisture, snow depth, and runoff. The models were run long enough beyond a state of quasi-equilibrium for meaningful statistics to be obtained. Time means of meteorological and hydrological quantities computed by the models compare favorably with observed climatic means. For example, the thermal structure of the model atmosphere is very similar to that of the actual atmosphere except in the Northern Hemisphere stratosphere; and the simulated distributions of the major arid regions over continents and the distributions of the rain belts, both in the Tropics and in middle latitudes, are successfully simulated by the models described in this paper. The increase in the horizontal computational resolution improved the distributions of mean surface pressure and precipitation rate in particular.