Cloud and Water Vapor Feedbacks to the El Niño Warming: Are They Still Biased in CMIP5 Models?
Abstract Previous evaluations of model simulations of the cloud and water vapor feedbacks in response to El Niño warming have singled out two common biases in the Phase 3 of Coupled Model Inter-comparison Project (CMIP3) models: an underestimate of the negative feedback from the shortwave radiation forcing of clouds (SWCRF) and an overestimate of the positive feedback from the greenhouse effect of water vapor. Here we check whether these two biases are alleviated in the Phase 5 of Coupled Model Inter-comparison Project (CMIP5) models. While encouraging improvements are found, particularly in the simulation of the negative SWCRF feedback, the biases in the simulation of these two feedbacks remain prevalent and significant. It is shown that bias in the SWCRF feedback correlates well with biases in the corresponding feedbacks from precipitation, large-scale circulation and longwave radiation forcing of clouds (LWCRF). By dividing CMIP5 models into two categories?high score models (HSM) and low score models (LSM)?based on their individual skills of simulating the SWCRF feedback, we further find that ocean-atmosphere coupling generally lowers the score of the simulated feedbacks of water vapor and clouds, but the LSM is more affected by the coupling than the HSM. We also find that the SWCRF feedback is simulated better in the models that have a more realistic zonal extent of the equatorial cold tongue, suggesting that the continuing existence of an excessive cold tongue is a key factor behind the persistence of the feedback biases in models.