Comparison of cloud forcing derived from the Earth Radiation Budget Experiment with that simulated by the NCAR community climate model

A comprehensive comparison of top of atmosphere radiative quantities from the Earth Radiation Budget Experiment (ERBE) with the same quantities from the latest version of the National Center for Atmospheric Research Community Climate Model (CCM) is presented. The ERBE data set offers a unique collection of top of atmosphere radiation fields for it includes clear‐sky radiation fields that have in the past not been available for such comparisons. Comparison between ERBE clear‐sky longwave fluxes and CCMl indicates larger outgoing flux in the model than measured by ERBE. This overestimation is ascribed to the prevalent dryness of the model. Comparison of clear sky albedo indicates good agreement over oceans and land. Total outgoing longwave flux also reflects the moisture deficiency of the model, but differences due to an underprediction of “effective” high cloud are also apparent. The clear‐sky and total fluxes are combined to form the cloud radiative forcing from the ERBE data and the CCM. Comparison of shortwave cloud radiative forcing indicates deficiencies in the model where marine stratus clouds are absent. Large longwave cloud forcing over the tropical deep convective regions in Indonesia and South America are present in the model but are underestimated compared with the ERBE results. Three regions, located over Indonesia, the equatorial Pacific, and the North Atlantic, are considered in detail. For the Indonesian region where deep convection is present, we consider the statistical correlation between the longwave cloud forcing and the shortwave cloud forcing from the ERBE data and CCM. Results indicate a near cancellation between the SWCF and LWCF for these regions, whereas the model predicts a net cooling. Another major area of discrepancy is over the North Atlantic and Pacific oceans where ERBE shows that clouds significantly reduce the solar heating of the oceans. While the model simulates this cooling, the magnitude is underpredicted by more than a factor of 2.