Impact of ENSO-Like Tropical Pacific Decadal Variability on the Relative Frequency of El Niño and La Niña Events

Abstract

Observational and modeling studies show that the relative frequency of El Niño and La Niña varies in association with El Niño–Southern Oscillation (ENSO)-like tropical Pacific decadal variability (TPDV), but the causality of the linkage remains unclear. This study presents evidence that ENSO-like TPDV affects the frequency of ENSO events, particularly of El Niño, through a set of climate model experiments. During the positive phase of TPDV, tropical Pacific warming relative to the Indian and Atlantic Oceans increases the occurrence of anomalous westerly winds over the western equatorial Pacific in late boreal winter-spring, triggering more El Niño and fewer La Niña events. The opposite happens for the negative TPDV phase. The La Niña frequency is also influenced by oceanic adjustments following El Niño, which tends to counteract the effect of wind changes. The mean state control of ENSO offers a potential opportunity for decadal predictions of climate extremes.