Assessment of the NASA GISS CMIP5 ModelE GCM Simulated Clouds and TOA Radiation Budgets Using CERES-MODIS, CALIPSO/CloudSat, and ISCCP Observations

To evaluate the GISS ModelE simulated global clouds and TOA radiation budgets, we have collected and processed NASA CERES and MODIS observations during the period 2000-2005. In detail, the 1x1 degree resolution monthly averaged SYN1 cloud product has been used with combined observations from both Terra and Aqua satellites, and degraded to a 2x2.5 degree grid box to match the GCM spatial resolution. The monthly means of the CERES EBAF radiation dataset have been used in this study, where the EBAF data are temporally interpolated using geostationary observations to infer the diurnal signal between CERES measurements. The GISS ModelE products were downloaded from the CMIP5 (Coupled Model Intercomparison Project Phase 5) being prepared for the IPCC-AR5. The model shows a high degree of accuracy in cloud fractions and radiation budgets when compared globally, however large differences are observed between the observations and the model when examined regionally. In particular, cloud fraction can be greatly underestimated or overestimated while Ice water path and liquid water path values are largely overestimated by the model in the southern mid-latitudes. This study examines these differences and the impact they have on the radiation budget. To determine whether these biases are caused by the microphysics or dynamics within the GCM, results will be partitioned by atmospheric states determined by Self Organizing Maps trained by reanalysis data.