Atlantic Warming Enhances the Influence of Atlantic Niño on ENSO.

The influence of Atlantic Niño on the following El Niño–Southern Oscillation becomes significant since mid‐1970s. However, exact mechanisms for this inter‐decadal change are still unclear. Here, we perform a set of model pacemaker experiments to probe the relative contributions of the changes in the Atlantic Niño itself and the mean‐state under global warming. The results suggest that the warmer background of the tropical Atlantic plays an essential role in enhancing local mean precipitation, inducing stronger divergence and low‐level easterlies in the Pacific. Under a favorable condition in the Pacific, even a weak Atlantic Niño‐related warming could promote the development of La Niña through cross‐basin Walker circulation and the Indian Ocean‐relayed Kelvin wave response. In contrast, the Atlantic Niño pattern change itself induces feeble convection anomalies in the western Atlantic, which cannot induce significant atmospheric response in the Pacific. These results imply an important modulation of global warming on the inter‐basin connection. Plain Language Summary: Climate phenomena in the three tropical oceans are tightly inter‐connected through atmospheric and oceanic pathways. The observations show that the influence of equatorial Atlantic sea surface temperature (SST) on the evolution of the following El Niño–Southern Oscillation displays a noticeable multi‐decadal change. The inter‐basin influence is negligible in early decades but becomes statistically significant since mid‐1970s. To understand this multi‐decadal change, the changes in the remote impacts of the tropical Atlantic Niño are divided into those related to the changes in the Atlantic Niño itself and the background mean SST. By comparing their relative contributions, we find the warmer climatological mean SST excites incremental precipitation around the western tropical Atlantic and Intertropical Convergence Zone (ITCZ), amplifying inter‐basin Walker circulation and the Indian Ocean relayed effect, and thus can more easily promote the evolution of La Niña in the following seasons. In contrast, despite the Atlantic Niño pattern broadens westwards in the recent decades, its induced‐feeble positive convection anomalies in the western Atlantic scarcely induce the atmospheric response over the tropical Pacific. Our results stress the vital role of the multi‐decadal SST warming in the tropical Atlantic and provide a plausible explanation for the multi‐decadal strengthening of this inter‐basin connection in recent decades. Key Points: The correlation between summer Atlantic Niño and the following El Niño–Southern Oscillation (ENSO) becomes significantly negative since 1976The warming‐induced tropical Atlantic mean‐state change, rather than the Atlantic Niño change itself, dominantly modulates the inter‐basin impact on ENSOThe climatological sea surface temperature/precipitation strengthened in the tropical Atlantic is important to exert the influence on ENSO [ABSTRACT FROM AUTHOR]