ENERGY AND WATER TRANSPORT IN CLIMATES SIMULATED BY A GENERAL-CIRCULATION MODEL THAT INCLUDES DYNAMIC SEA-ICE

We analyze energy and water transport in present, doubled CO2, and tri pled CO2 climates simulated by the Mark 2 CSIRO nine-level general cir culation model with a mixed layer ocean. The model differs from the Ma rk 1 version by the inclusion of dynamic sea ice, a semi-Lagrangian wa ter vapor transport, and an enhanced land-surface scheme, and it inclu des prescribed ocean heat transport. We describe a 30-year climatology of the 1xCO(2) simulation, emphasizing the sea ice and the mean merid ional energy and water transport. The ice depths, concentrations, and velocities are moderately realistic in both hemispheres. Poleward ener gy transport is inferred (calculated indirectly from vertical energy f luxes) for both the atmosphere and ocean, although the oceanic flux is much weaker than observational estimates for the southern hemisphere. Atmospheric water transport is also poleward outside the tropics and compares well with observations. Energy transport within the ice layer has been evaluated by both direct and indirect methods. As it is larg ely due to the latent heat of ice formation, it is closely proportiona l to the water transport by ice. The meridional transports by ice of b oth energy and water are relatively important at high latitudes. The d ivergence of the ice energy transport corresponds to a significant com ponent of the surface energy budget, reaching +/-10 W m(-2) or more at some polar locations. The equilibrated doubled CO2 global mean surfac e warming of the Mark 2 mixed layer model is 4.3 degrees C. The reduct ion from the Mark 1 result (4.8 degrees C) follows largely from a 40% reduction of the warming over high-latitude oceans. This is attributed to the presence of dynamically induced leads in the ice cover. The eq uilibrated warming for 3xCO(2) is 6.8 degrees C. The model atmosphere transports less heat poleward in the doubled CO2 climate, largely as a response to increased solar radiation absorbed at high latitudes. Thi s behavior contrasts with the change at CO2 doubling in a transient si mulation by the Mark 2 model coupled to a full ocean model, in which h eat is taken up in the midlatitudes, particularly by the Southern Ocea n, and supplied by a net top-of-atmosphere radiative imbalance distrib uted over all latitudes (global mean, 1.8 W m(-2)). The atmospheric wa ter transport is enhanced by 10-20% in the wanner climates at most lat itudes.