Tropical Atlantic and Pacific sea surface temperature gradients modulate the summer Atlantic Niño-winter ENSO...

The relationship between the boreal summer Atlantic Niño and subsequent winter El Niño-Southern Oscillation (ENSO) has strengthened in recent decades, but the underlying mechanism remains unclear. In this study, we identified tropical Atlantic and Pacific sea surface temperature (SST) gradients as the key drivers of the summer Atlantic Niño-winter ENSO connection. In detail, zonal SST gradients over the tropical Atlantic, driven by wind-evaporation-SST feedback, regulate the Atlantic Niño-ENSO connection by modulating the cross-basin Walker circulation between the tropical western Atlantic and eastern Pacific. Under weak zonal SST gradients, the Gill-Matsuno-type response to the Atlantic Niño exhibits stronger ascending motion over the tropical western Atlantic than under strong gradient conditions. The meridional SST gradients over the tropical eastern Pacific enhance anomalous descent that helps to establish the cross-basin Walker circulation. Consequently, the enhanced Pacific Walker circulation contributes to the development of La Niña and strengthens the Atlantic Niño-ENSO connection. Model sensitivity experiments confirm this mechanism. This study has identified new drivers of tropical Atlantic-Pacific cross-basin linkages that have significant implications for ENSO prediction.