Sea surface temperature gradients switch the Atlantic Niño's link to ENSO on and off

When a warm "Atlantic Niño" develops in the tropical Atlantic one summer, the tropical Pacific is more likely to tip into La Niña the following winter—but only sometimes. For roughly half a century the link vanished from the observational record, then reemerged. A study published in The Innovation on July 10, 2026 identifies the switch: the shape of sea surface temperature gradients in two tropical oceans.

ENSO—El Niño–Southern Oscillation, the Pacific's dominant year-to-year climate fluctuation—drives droughts, floods, and heat waves worldwide. Its Atlantic counterpart, the Atlantic Niño, has long been suspected of carrying an early signal for ENSO, yet the connection is unstable. Analyzing over a century of observations, a team led by researchers at Yunnan University found that the summer Atlantic Niño and the subsequent winter's ENSO were significantly correlated during 1894–1925 and 1984–2009, but not during 1928–1981.

The explanation lies in gradients. The tropical Atlantic's east–west sea surface temperature gradient is shaped by the wind–evaporation–SST (WES) feedback: when the feedback weakens, so does the gradient. A weak Atlantic gradient alters how the atmosphere responds to an Atlantic Niño, strengthening rising motion over the tropical western Atlantic. At the same time, a strong north–south temperature gradient in the eastern tropical Pacific enhances sinking motion. Together, the rising and sinking branches lock into a Walker circulation spanning both basins—the same kind of atmospheric loop that links the western Pacific's warm pool with the cold eastern equatorial Pacific. Once this cross-basin circulation is established, an Atlantic Niño can promote La Niña in the Pacific the following winter, tightening the connection between the two oceans.

Model sensitivity experiments, in which the researchers modified the temperature gradients, supported the mechanism: the favorable gradient configuration built up the cross-basin circulation, while the opposite configuration left the two oceans effectively decoupled.

The finding gives seasonal forecasters a physical explanation for when the Atlantic's "preview" of ENSO can be trusted—and when it cannot. It also helps explain why the same Atlantic warming can matter greatly in one decade and little in the next. The authors note that future work should further quantify how each ocean basin's temperature gradients contribute to cross-basin interactions—knowledge they argue could sharpen ENSO prediction and climate risk warnings.