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Abstract

Characterizing cloud physical and radiative properties, as well as their responses to external forcings (e.g.,  anthropogenic aerosols, global warming, etc.), remains a major uncertainty in projecting Earth's radiation budget and hydrological cycle at global, regional, and local scales. Here we show that remarkable improvements on simulations of present-day atmosphere can be achieved through model retuning and better integration of model physical parameterizations. We compare the Energy Exascale Earth System Model (E3SM) Atmosphere Model version 1 (EAMv1) and a re-calibrated model configuration, finding that when processes regulating cloud lifecycle are calibrated to produce a much more realistic present-day cloud climatology, many of the common and long-standing biases in global models, such as the northern hemisphere surface warm bias, the surface wind stress bias over southern ocean, the precipitation bias in the tropics, the double ITCZ bias, the dry bias over Amazon, the trade wind bias, and the bias of long-range transport of aerosols, are reduced significantly at the same time. Furthermore, compared to EAMv1, this model configuration shows significantly lower aerosol indirect forcing and total cloud feedback (to surface warming), and significantly higher total adjusted forcing, suggesting a much weaker equilibrium climate sensitivity.

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