Distinct Contributions of Tropical and Extratropical Coupling Processes to ENSO Complexity

Not all El Niño–Southern Oscillation (ENSO) events are the same. An El Niño (La Niña) event may be followed by a neutral state to result in an ENSO episode, by a La Niña (El Niño) event to result in an ENSO cycle, or by another El Niño (La Niña) event to result in a multi-year ENSO event. In this talk, a new framework will be presented to explain a source of this ENSO complex.

In this framework, ENSO complexity is linked to two key coupling mechanisms in the tropical and extratropical Pacific. The interplay of these processes can explain how the different ENSO evolution (episodes, cycles, and multi-year events) are produced. The study finds the extratropical coupling process works to increase ENSO complexity while the tropical coupling process acts to reduce the complexity. The framework proposed in this study can also explain why the properties of El Niño and La Niña can be asymmetric to each other.

This talk will also discuss the reason why the extratropical coupling process can increase the ENSO complexity and El Niño-La Niña asymmetries as well as the application of this ENSO complexity framework in climate model evaluations.