SENSITIVITY OF THE SIMULATED CLIMATE TO A DIAGNOSTIC FORMULATION FOR CLOUD LIQUID WATER

The accurate treatment of clouds and their radiative properties is wid ely regarded to be among the most important problems facing global cli mate modeling. A number of the more serious systematic simulation bias es in the NCAR Community Climate Model (CCM2) appear to be related to deficiencies in the treatment of cloud optical properties. In this pap er, a simple diagnostic parameterization for cloud liquid water is pre sented. The sensitivity of the simulated climate to this alternative f ormulation, both in terms of mean climate metrics and measures of the climate system response, is illustrated. Resulting simulations show si gnificant reductions in CCM2 systematic biases, particularly with resp ect to surface temperature, precipitation, and extratropical geopotent ial height-field anomalies. Many aspects of the simulated response to ENSO forcing are also substantially improved.