Evaluation of Cloud Properties in Seven SCMs under Updraft and Downdraft Regimes

This study evaluates the overall performances of seven SCMs (CAM 3, 4, 5; GFDL AM2, 3; GISS and ECMWF) by comparing simulated cloud fraction, in-cloud liquid and ice water content (LWC and IWC), and cloud radiative forcings with observations at the ARM SGP site from 01 January 1999 to 31 December 2001. The evaluation focuses on the model performance at different dynamical regimes classified by 500-hPa large-scale vertical pressure velocity. It is shown that the simulated cloud profiles of the seven SCMs, especially three CAM SCMs, are differently biased from the observation under updraft and downdraft regimes. Analysis of the variations of the cloud fraction, LWC, IWC and cloud radiative forcings under the two dynamical regimes indicates that all these SCMs can reasonably capture the observed seasonal variations of cloud fraction and cloud radiative forcings, despite different biases in magnitudes. However, the seasonal variations of simulated cloud water content deviate significantly from the observation for all the models. Further analysis shows that the model biases in cloud fraction are the dominant contributor to the biases in the cloud radiative forcings (especially longwave) at TOA and the surface.