AN ATMOSPHERIC ENERGY-MOISTURE BALANCE MODEL - CLIMATOLOGY, INTERPENTADAL CLIMATE-CHANGE, AND COUPLING TO AN OCEAN GENERAL-CIRCULATION MODEL

An atmospheric model incorporating energy and moisture balance equatio ns is developed for use in process studies of the climate system, Give n the sea surface temperature and specified surface wind field, the at mospheric model calculates the surface fields of air temperature, spec ific humidity, as well as heat and freshwater fluxes. The inclusion of the moisture balance in the atmospheric model allows the effects of l atent; heat transport to be included explicitly in the model, Under fi xed climatological sea surface temperature (SST) and surface wind cond itions, surface air temperatures, specific humidities, and surface flu xes are comparable to direct estimates. Precipitation compares less fa vorably with observations, As an extension to the climatological forci ng case, we conduct a simple perturbation experiment in which the 1955 -1959 pentad is compared to the 1970-1974 pentad by driving the model under the respective SST fields. The model exhibits a global air tempe rature decrease in the latter pentad of 0.27 degrees C (comparable to direct estimates) with cooling in the northern hemisphere and warming in the southern hemisphere, Such large-scale cooling in our atmospheri c model is driven by equivalent local changes in the prescribed SST fi elds, subsequently smoothed by atmospheric diffusion of heat, The inte rpentadal modeled differences are shown to be quite robust through mod el experiments using parameters representative of several different un realistic climatologies. The resulting interpentadal difference fields change remarkably little even when the background state has changed d ramatically, This emphasizes the almost linear response of the atmosph eric model to the imposed SST changes. The atmospheric model is also c oupled to an ocean general circulation model without the need for flux adjustments, This coupled climate model faithfully represents deep wa ter formation in the North Atlantic and Southern Ocean, with. upwellin g throughout the Pacific and Indian Oceans. Water mass characteristics in the vertical compare very favorably with direct observations.