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Abstract: The Radiative-Convective Equilibrium Model Intercomparison Project (RCEMIP) is an intercomparison of multiple types of numerical models, including atmospheric general circulation models (GCMs), cloud-resolving models (CRMs), global cloud-resolving models (GCRMs), large eddy simulation models (LES), and single column models (SCMs), configured in radiative-convective equilibrium (RCE). RCE is an idealization of the tropical atmosphere that has long been used to study basic questions in climate science, and is employed here to investigated the response of clouds and convective activity to warming, cloud feedbacks and climate sensitivity, and the aggregation of convection and its role in climate. Results are presented from the RCEMIP ensemble of more than 30 different models. The robustness of the RCE state across the RCEMIP ensemble is assessed, in terms of mean profiles of temperature, humidity, and cloudiness, and the occurrence of self-aggregation is identified. While there are significant differences across the RCEMIP ensemble in the representation of humidity and cloudiness, nearly all models exhibit self-aggregation and there is agreement that self-aggregation acts to dry the atmosphere and reduce high cloudiness. The dependence of cloudiness and the degree of self-aggregation on SST and the resulting influence on the climate sensitivity of the RCE state is also compared across the RCEMIP ensemble. High clouds tend to rise and warm slightly with warming, and in a majority of models, decrease in extent. There is no clear tendency for either an increase or decrease in self-aggregation with warming, but changes in self-aggregation with warming partially explain the extreme spread in simulated climate sensitivities across the RCEMIP ensemble.
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