Influences on surface energy fluxes in simulated present and doubled CO2 climates

The surface energy fluxes simulated by the CSIRO9 Mark 1 GCM for present and doubled CO2 conditions are analyzed. On the global scale the climatological flux fields are similar to those from four GCMs studied previously. A diagnostic calculation is used to provide estimates of the radiative forcing by the GCM atmosphere. For 1xCO(2), in the global and annual mean, cloud produces a net cooling at the surface of 31 W m(-2). The clear-sky longwave surface greenhouse effect is 311 W m(-2), while the correspond ing shortwave term is -79 W m(-2). As for the other GCM results, the CSIRO9 Delta CO2 surface warming (global mean 4.8 degrees C) is closely related to the increased downward longwave radiation (LW down arrow). Global mean net cloud forcing changes little. The contrast in warming between land and ocean, largely due to the increase in evaporative cooling (E) over ocean, is highlighted. In order to further the understanding of influences on the fluxes, simple physically based linear models are developed using multiple regression. Applied to both 1xCO(2) and Delta CO2 December-February mean tropical fields from CSIRO9, the linear models quite accurately (3-5 W m(-2) for 1xCO(2) and 2-3 W m(-2) for Delta CO2) relate LW down arrow and net shortwave radiation to temperature, surface albedo, the water vapor column, and cloud. The linear models provide alternative estimates of radiative forcing terms to those from the diagnostic calculation. Tropical mean cloud forcings are compared. Over land, E is well correlated with soil moisture, and sensible heat with air-surface temperature difference. However an attempt to relate the spatial variation of LW up arrow within the tropics to that of the nonflux fields had Little success. Regional changes in surface temperature are not linearly related to, for instance, changes in cloud or soil moisture.