Enhanced impact of the Aleutian Low on increasing the Central Pacific ENSO in recent decades

Abstract

In this study, we reveal a marked enhanced impact of the early-spring Aleutian Low (AL) on the following winter El Niño and Southern Oscillation (ENSO) after the late-1990s. This enhanced impact of the early-spring AL may have an important contribution to the increased emergence of the central Pacific ENSO during recent decades. 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 associated westerly (easterly) wind anomalies to the south side of the subtropical anomalous cyclone (anticyclone) over the tropical western Pacific contribute to occurrence of central Pacific-like El Niño (La Niña) in the following winter via tropical Bjerknes feedback. Further, the subtropical anomalous cyclone (anticyclone) leads to sea surface temperature (SST) increase (decrease) in the equatorial Pacific in the following summer via wind-evaporation-SST (WES) feedback, which further contributes to succeeding central Pacific-like El Niño (La Niña). Enhanced impact of early-spring AL on ENSO is attributable to enhancement of the mean circulation over the North Pacific, which leads to increased wave-mean flow interaction and strengthened WES feedback after the late-1990s. The results offer the potential to advance our understanding of the factors for the reduced prediction skill of ENSO since the late-1990s.