Climate sensitivity and cloud feedback dependence on scale and strength of mean-state Walker circulation

Idealized models have been used with resounding success to understand robust physics of the climate. A traditional aquaplanet with zonally symmetric sea surface temperatures (SSTs) has many realistic circulation features of Earth’s climate, like a meridional Hadley circulation. But without continents and the associated zonal SST gradients, it lacks a Walker circulation and the radiatively important stratocumulus clouds that form in the subsiding branch. Here, we present an intermediate along this model hierarchy, an aquaplanet with mock-Walker circulation, to investigate the role of cloud-circulation coupling on climate feedbacks and sensitivity. In our novel “stratocu-planet,” the circulation strength and stratocumulus amount increase with the SST perturbation strength and decrease with the perturbation length scale. We show how climate sensitivity and feedbacks, particularly the cloud feedback, respond to changes in the mean-state circulation and discuss the implications of these results with regard to the past and future pattern of Pacific warming.