Analysis of Cloud Properties Associated with Tropical Convection in Climate Models and Satellite Data

Cloud properties associated with tropical convection are analyzed for 11 models participating in Cloud Feedback Model Intercomparison Project Phase 1 (CFMIP1) in comparison with International Satellite Cloud Climatology Project (ISCCP) and other satellite observations and reanalysis datasets. Cloud properties are analyzed for different regimes of large-scale circulation field sorted by monthly mean of pressure coordinated vertical velocity at 500 hPa as an index of large-scale circulation. The present analysis is focused on warm oceanic regions with sea surface temperatures above 27°C where convection is active. The warm oceanic regions cover the vertical motion regimes ranging from strong ascent to weak descent. The ISCCP simulator outputs are used to evaluate cloud properties in the models. Cloud amount of optically thick high-clouds with optical thicknesses (τ) ≧ 3.6 and cloud-top pressure (CTP) ≦ 440 hPa is overestimated in the strong ascent regime while that of optically thin high-clouds with τ < 3.6 is underestimated for all the regimes. Cloud amount of optically thick low-clouds with CTP ≧ 680 hPa is overestimated in the weak vertical motion regime as well in some models. The relevance of cloud amount bias to cloud radiative effect bias is discussed. Observations show that optically thick clouds in the strong ascent regime often have tops around 180–310 hPa. In many models, the cloud top often reaches higher altitude compared to the observations. The tendency can especially be seen in the models adopting the moisture accumulation type scheme presumably due to excessively deep convection. Comparison of upward motion strength among the models and reanalyses suggests that cumulus parameterization performs better when entrainment rate is varied with large-scale environmental fields to reduce the convection deepness where necessary.