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

摘要

Observational and modeling studies show that the relative frequency of El Nino and La Nina varies in association with El Nino-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 Nino, 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 Nino and fewer La Nina events. The opposite happens for the negative TPDV phase. The La Nina frequency is also influenced by oceanic adjustments following El Nino, 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.