Abstract
Although societally important, extreme precipitation is difficult to represent in climate models. This study shows one robust aspect of extreme precipitation across models: extreme precipitation over tropical oceans is strengthened through a positive feedback with cloud-radiative effects. This connection is shown for a multi-model ensemble with experiments that make clouds transparent to longwave radiation. In all cases, tropical extreme precipitation reduces without cloud-radiative effects. Qualitatively similar results are presented for one model using the cloud-locking method to remove cloud feedbacks. The reduced extreme precipitation without cloud-radiative feedbacks does not arise from changes in the mean climate. Rather, evidence is presented that cloud-radiative feedbacks enhance organization of convection and most extreme precipitation over tropical oceans occurs within organized systems. This result suggests that climate models must correctly predict cloud structure and properties, as well as capture the essence of organized convection in order to accurately represent extreme rainfall.
Highlights
Cloud-radiative effects (CREs) are defined by the difference between the all-sky radiation flux and the clear-sky flux, and can be divided into shortwave (SW) and longwave (LW) components
Climate models have lately been adapted for radiativeconvective equilibrium (RCE) experiments, and show similar convective organization as the high-resolution models[20,21,22]
Work has shown that in climate models, CREs impact aspects of organized convection[12] and that the representation of extreme precipitation depends on the degree of convective organization[34]
Summary
Cloud-radiative effects (CREs) are defined by the difference between the all-sky radiation flux and the clear-sky flux, and can be divided into shortwave (SW) and longwave (LW) components. Climate models have lately been adapted for RCE experiments, and show similar convective organization ( on larger scales) as the high-resolution models[20,21,22] Some of these studies have pointed to different mechanisms of convective aggregation than the CRM studies; for example, Coppin and Bony[23] show how low-level cloud effects drive aggregation at cooler surface temperatures. Work has shown that in climate models, CREs impact aspects of organized convection[12] and that the representation of extreme precipitation depends on the degree of convective organization[34]. The idealized aquaplanet simulations shown, b show the realistic AMIP configurations forced by organization is thought to be connected to extreme precipitation, it seems natural to ask how cloud-radiative feedbacks influence extreme precipitation. The weakening and widening of the rain belts when CRE is deactivated is similar in experiments with both SW and LW effects removed[38,39]
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