Decadal variations of Pacific Walker circulation tied to tropical Atlantic–Pacific trans-basin SST gradients

Abstract

During the modern satellite-monitoring era since ∼1979, the observed Pacific Walker circulation (PWC) presented a pronounced strengthening and robust westward-shifting, defying the model-projected weakening response to anthropogenic warming. The exact cause for the PWC decadal intensification and the corresponding observation-model disagreement remains indecisive. Using two targeted experiments wherein sea surface temperature (SST) anomalies in the tropical eastern Pacific and North Atlantic are separately restored to follow the observed history, we reveal that the North Atlantic-only SST warming and the tropical eastern Pacific-only SST cooling contribute partly to the PWC decadal adjustment. The North Atlantic SST warming triggers a significant westward displacement of PWC, while the tropical eastern Pacific SST cooling drives mainly the associated shifts of the large-scale atmospheric surface pressure centers. Further, we identify that the tropical Atlantic–eastern Pacific trans-basin SST gradients have dominated the PWC decadal variations over the past century. Our results highlight that a reliable representation of the simulated inter-basin warming contrast between the tropical Atlantic and the tropical eastern Pacific SSTs may be influential in correcting future projections of the PWC strength.