Cloud - SST feedback simulated from GCM and comparison with observations

Marine stratocumulus clouds ( MSCs ) cover a large fraction of horizontal area over the global ocean and strongly cool the Earth-atmosphere system by reflecting incoming solar radiation. In a typical climate change scenario of doubled carbon dioxide, global warming can be fully offset if the fraction of MSCs increases by 3%. Thus, reasonable GCM simulation of marine stratocumulus clouds is essential for correct assessment of climate change, but it remains as a difficult issue since the properties of MSCs are controlled by complex sub-grid scale feedback processes involving radiation, convection, and entrainment within atmospheric boundary layer. In this study, we report our recent effort to improve global cloud simulations using University of Washington Planatary Boundary Scheme (UW-PBL) embedded in the most recent version of the NCAR Community Atmospheric Model. The simulated cloud climatology is compared with the observations. In turn, by comparing simulations with climatological SST and +2K SST perturbations, the strength of simulated cloud-SST feedback is estimated and compared with the observed cloud-SST feedback estimated from the ship-observed turbulent heat and moisture fluxes and satellite-derived radiative flux data at the surface.