Intensified annual cycle of tropical Atlantic sea surface temperature regulates Pacific cooling

Recent counterintuitive cooling in the eastern tropical Pacific, with prolonged impacts on global climate, has perplexed the climate community regarding its underlying causes. While previous studies have proposed many potential explanations, the present study identifies a distinct and previously underappreciated driver. Here, by conducting a series of sensitivity experiments, we demonstrate that an intensified annual cycle of sea surface temperature in the tropical Atlantic can also drive a cooling in the eastern tropical Pacific over the past decades. The intensified annual cycle significantly alters the distribution of seasonal precipitation, leading to a net reduction of annual mean precipitation in the equatorial Atlantic. This dry state is accompanied by lower-troposphere divergence, inducing easterly anomalies along the equatorial Pacific and ultimately leading to a strong Pacific cooling. Our findings unveil a previously overlooked role of the tropical Atlantic annual cycle change in regulating tropical Pacific climate and shaping large-scale climate patterns. Recent observed cooling in the Pacific Ocean is driven by an intensified annual cycle of sea surface temperature in the tropical Atlantic altering the distribution of seasonal precipitation, according to analyses of idealized experiments and climate model simulations.