BAROCLINIC ADJUSTMENT - A COMPARISON BETWEEN THEORY, OBSERVATIONS, AND MODELS

Isentropic slopes calculated from Northern Hemisphere analyses of the zonal mean state of the atmosphere are compared with isentropic slopes calculated from baroclinic adjustment theory. In midlatitudes, the is entropic slopes are relatively close to the adjusted values in the lay er from 2 to 7 km (800 to 400 mb). They also have very little variatio n in latitude and season, which implies that baroclinic eddy fluxes su pply a strong negative feedback to changes in isentropic dopes. The ve rtical structure of the temperature field in the ''adjusted'' layers a nd the location of the layers suggest that vertical eddy heat fluxes p lay a significant role in this feedback process. Isentropic slopes are also calculated from simulations of the current climate by the GISS M odel II GCM and the NCAR CCM2. Both models have regions of apparent ba roclinic adjustment similar to that in the Northern Hemisphere atmosph ere. However, compared to the observations, the agreement of the simul ations with baroclinic adjustment theory is not as good, and the isent ropic slopes show stronger latitudinal and seasonal variations. The di screpancies are associated primarily with errors in the models' meridi onal temperature gradients in the lower troposphere in midlatitudes. T he seasonal changes in these gradients are much larger than in the obs ervations, particularly in the CCM2, even though the model simulations were constrained by climatological sea surface temperatures.