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

Observational and modeling studies show that the relative frequency of El Niño and La Niña events varies in association with ENSO-like tropical Pacific decadal variability (TPDV). However, the causality of TPDV and ENSO changes 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 forced with surface heat flux anomalies associated with TPDV. 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, triggering more El Niño and less La Niña. The decrease in La Niña frequency is partly counteracted by an increase in La Niña following El Nino. The mean state control of ENSO offers a potential opportunity to predict decadal changes in climate extremes.