Heat Balance Statistics Derived from Four-Dimensional Assimilations with a Global Circulation Model

Abstract

A method is demonstrated for evaluating global and zonally averaged heat balance statistics based on a four-dimensional assimilation with an atmospheric general circulation model (GCM). The procedure, which provides observationally constrained model diagnostics, uses the GCM of NASA's Goddard Laboratory for Atmospheric Sciences to evaluate the atmospheric heat balance for the February 1976 Data Systems Test period. The global distribution of the adiabatic and diabatic components of the heat balance are obtained by sampling the continuous GCM assimilation shortly after the insertion of conventional synoptic observations. Sampling times of 6 and 9 h after data insertion were chosen to provide adequate damping of high-frequency oscillations in the vertical velocity field caused by the data insertion. Salient features of the February 1976 analysis include the following: Maximum rising motion in the mean vertical velocity field at 500 mb over South America, south-central Africa, Australia and the Indonesian archipelago. These regions also were characterized by large values of diabatic heating due to convective latent heat release. The cyclogenetically active regions over the North Atlantic and North Pacific oceans were characterized by maxima in latent heat release due to supersaturation cloud formation, and also maxima in the upward and northward transient eddy heat fluxes. In contrast, the continental west coasts showed a tendency for large downward and southward transient eddy beat fluxes. Some differences are obtained between the heating rates calculated with the model parameterizations and through a residual method. Other shortcomings of the procedure include data deficiencies in the Southern Hemisphere, which cause the results to be comparatively more model dependent in the high southern latitudes. The potential applicability of this method of analysis to the recently acquired FGGE data is noted.