Effect of ENSO on Clouds and Cloud Radiative Effects in CMIP5 Models

This study evaluates the CMIP5 AMIP simulations of the effect of ENSO on top-of-atmosphere (TOA) cloud radiative effects (CREs) in the tropics, and investigates the linkage between the model simulations of TOA CREs and their representations of 3-D clouds by examining CALIPSO and ISCCP simulator output from the CFMIP Observation Simulator Package. Satellite-based observations including the CERES EBAF radiative fluxes and reanalysis are used for the model evaluation.

The results show that the CMIP5 models perform fair well in simulating ENSO associated CRE anomalies in the central tropical Pacific, yet show considerably weaker shortwave and longwave CRE anomalies in the western tropical Pacific. The good model performance in the central tropical Pacific is a result of compensating errors between smaller changes in thin high clouds and larger changes in medium and thick high clouds, whereas the weaker anomalies over the western tropical Pacific is due to considerably smaller changes in thin and medium high clouds. The above model biases in ENSO associated anomalies result from the model biases in their mean clouds which are optically thicker, and show less high cloud over maritime Continent and more high cloud over transitional trade cumulus regions. Lastly, the relative roles of model biases in cloud amount, altitude and optical thickness anomalies in contributing to their biases in ENSO associated TOA CRE anomalies are quantified using the Fu-Liou radiative transfer model.