SIMULATIONS OF SOUTHERN AFRICAN CLIMATE BY EARLY GENERATION GENERAL-CIRCULATION MODELS

The present-day performance of six early generation general circulatio n models is assessed for the southern African region. The validation f ocuses an the simulation of the pattern and magnitude of observed surf ace air temperatures, mean sea-level pressures and precipitation. Calc ulated errors in the simulation of southern African climate are genera lly characteristic of those reported elsewhere for this generation of mined-layer slab-ocean equilibrium climate models. In each case, error s in the simulation of a particular variable are related to the repres entation in the models of physical processes important to the region's climate. Surface air temperature simulations are sensitive to the par ameterization of cloud radiative feedbacks and cumulus convection. Acc urate representation of the equator-to-pole surface pressure gradient is strongly dependent on the inclusion of a gravity wave drag term in the parameterization of surface stress. Convective precipitation is po orly simulated by the coarse-resolution models considered in this anal ysis. Consequently the ability of the models to represent the pattern of rainfall seasonality is assessed as a means of evaluating the respo nse of rainfall patterns to large-scale circulation changes associated with the annual cycle of radiation. Accurate simulations of specific variables by individual models are identified. In respect of all three variables considered one model is shown to provide the most accurate representation of present-day southern African climate.