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Abstract

Cloud radiative effects (CREs) are known to play a central role in governing the long-term mean distribution of sea-surface temperatures (SSTs). Very recent work suggests that CREs may also play a role in governing the variability of SSTs in the context of the El Niño/Southern Oscillation. Here, the authors exploit numerical simulations in the Max Planck Institute Earth System Model with two different representations of CREs to demonstrate that coupling between CREs and the atmospheric circulation has a much more general and widespread effect on tropical climate than that indicated in previous work.The results reveal that coupling between CREs and the atmospheric circulation leads to robust increases in SST variability on timescales longer than a month throughout the tropical oceans. Remarkably, cloud/circulation coupling leads to more than a doubling of the amplitude of decadal-scale variability in tropical-mean SSTs. It is argued that the increases in tropical SST variance derive primarily from the coupling between SSTs and shortwave CREs: Coupling increases the memory in shortwave CREs on hourly and daily timescales, and thus reddens the spectrum of shortwave CREs and increases their variance on timescales spanning weeks to decades. Coupling between SSTs and CREs does not noticeably affect the variance of SSTs in the extratropics, where the effects from variability in CREs on the surface energy budget are much smaller than the effects from the turbulent heat fluxes. The results indicate a basic but critical role of CREs in climate variability throughout the tropics.