Why does the CP El Niño less frequently evolve into La Niña than the EP El Niño

Author(s): He, S; Yu, JY; Yang, S; Fang, SW | Abstract: During 1958–2017, the Central-Pacific (CP) El Nino evolved into La Nina less frequently (38%) than the Eastern-Pacific (EP) El Nino (75%). Composite analyses reveal that the reversal of zonal wind anomalies in the tropical western Pacific is the key mechanism for the EP El Nino's transitions to La Nina. This reversal induces oceanic Kelvin waves to promote the La Nina onset. This reversal mechanism is often triggered by the Indo-Pacific teleconnection produced by the EP El Nino. Consequently, the EP El Nino 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 Nino to La Nina via local processes. However, the subtropical teleconnection of the CP El Nino prevents this mechanism from occurring and often causes the nontransitional evolution for the CP events.