Global Model Simulation of Clouds in CMIP5 and CMIP3

1. Global Model Simulation of Clouds in CMIP5 and CMIP3 Axel Lauerand Kevin Hamilton J. Climate, in press The Coupled Model Intercomparison Project phase 3 (CMIP3) and 5 (CMIP5) results allow evaluation of state-of-the art global climate models from the world’s major research centers circa 2005 and 2011. A major challenge is simulation of realistic cloud fields. Figure 1 shows observed annual mean cloud properties and biases in the CMIP simulations representing the late 20th century. Although the multi-model mean results shown are better than the individual model results (not shown), they still display very large biases. Overall the CMIP5 model results are improved only modestly over those from the older CMIP3 models. The simulated biases in cloud liquid water path in fully coupled ocean-atmosphere models and in “AMIP” experiments with imposed observed ocean temperatures are shown in Figure 2. The coupled and AMIP runs have remarkably similar biases, directly implicating the treatments of subgrid-scale cloud and boundary layer processes in the poor cloud simulations by state-of-the-art global models. Fig. 1. Biases in simulated long term annual mean cloud liquid water path (top) and fractional cloud amount (bottom). Satellite observations are shown at right, and the biases from the observations are shown for the multimodel mean for CMIP3 (left) and CMIP5 (center). Fig. 2. Comparison of the CMIP5 multimodel mean bias of simulated cloud liquid water path in the full coupled atmosphere-ocean models (left) and in experiments run with prescribed observed ocean surface temperatures (right).