A new perspective on increased emergence of Central Pacific ENSO in the recent two decades

Abstract

Abstract In this study, we provide a new perspective on the recent increased emergence of the central Pacific type of El Niño and Southern Oscillation (ENSO). Our results indicate that early-spring Aleutian Low (AL) intensity has a remarkable impact on the following winter ENSO especially after the late-1990s. Decrease (increase) in the early-spring AL strength tends to induce an anomalous cyclone (anticyclone) over subtropical North Pacific via wave-mean flow interaction. The anomalous cyclone (anticyclone) leads to sea surface temperature (SST) increase (decrease) in the equatorial Pacific in the following summer via wind-evaporation-SST feedback and trade wind charging mechanism, which further contributes to succeeding central Pacific-like El Niño (La Niña). This remarkable AL’s impact on ENSO is attributable to enhancement of the background trade winds, which is related to changes of both the AMO and NPGO from positive to negative phases around the late-1990s. In contrast, global warming is suggested to have a negative effect on the recent increased connection of the early-spring AL with the following winter ENSO. The results offer the potential to advance our understanding of the factors that explain decrease of the prediction skill of ENSO since the late-1990s.