资源环境科技发展态势分析平台

The observed El Niño and La Niña exhibit different complexities in their event‐to‐event transition patterns. The El Niño is dominated in order by episodic, cyclic, and multi‐year transitions, but the reversed order is found in the La Niña. A subtropical Pacific onset mechanism is used to explain this difference. This mechanism triggers El Niño/La Niña events via subtropical processes and is responsible for producing multi‐year and episodic transitions. Its nonlinear responses to the tropical Pacific mean state result in more multi‐year transitions for La Niña than El Niño and more episodic transitions for El Niño than La Niña. The CMIP5/6 models realistically simulate the observed transition complexity of El Niño but fail to simulate the transition complexity of La Niña. This deficiency in CMIP5 models arises from a weaker than observed subtropical onset mechanism and a cold bias in the tropical Pacific mean sea surface temperatures in the models.