Evaluation and attribution of shortwave feedbacks to ENSO in CMIP6 models

The shortwave (SW) feedback to El Ni & ntilde;o-Southern Oscillation (ENSO) is one of the largest biases in climate models, as the feedback includes atmosphere-ocean interactions and cloud processes. In this study, the performance of SW feedback over tropical Pacific in 19 models from the 6th Coupled Model Intercomparison Project (CMIP6) is evaluated and the biases are attributed using the historical and Atmospheric Model Intercomparison Project (AMIP) runs and two coupled assimilation experiments. The results demonstrate that while superior to CMIP5 counterparts, most CMIP6 models still underestimate the strength of SW feedback. The underestimates of SW feedback arise mainly from the biased feedbacks to El Ni & ntilde;o in the four models with relatively better skills, while from both underestimated negative feedbacks to El Ni & ntilde;o and overestimated positive feedbacks to La Ni & ntilde;a in other models, which reproduce better seasonal variations than corresponding CMIP5 models. Furthermore, the SW feedback bias is connected to weak convective/stratiform rainfall feedback, which is sensitive/insensitive to sea surface temperature (SST) biases during El Ni & ntilde;o/La Ni & ntilde;a. The total rainfall feedbacks and dynamical feedbacks are underestimated in the historical runs, more than in CMIP5. Finally, the causes and relationships between feedbacks and mean states are investigated.