UC Irvine

During 1958–2017, the Central-Pacific (CP) El Niño evolved into La Niña less frequently (38%) than the Eastern-Pacific (EP) El Niño (75%). Composite analyses reveal that the reversal of zonal wind anomalies in the tropical western Pacific is the key mechanism for the EP El Niño's transitions to La Niña. This reversal induces oceanic Kelvin waves to promote the La Niña onset. This reversal mechanism is often triggered by the Indo-Pacific teleconnection produced by the EP El Niño. Consequently, the EP El Niño often experiences the transitional evolution. For the CP events, the southward shift of westerly anomalies in the tropical central Pacific is the key mechanism for transitions from El Niño to La Niña via local processes. However, the subtropical teleconnection of the CP El Niño prevents this mechanism from occurring and often causes the nontransitional evolution for the CP events.