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Statistical occurrence and mechanisms of the 2014–2016 delayed super El Niño captured by a simple dynamical model

Thual, Sulian, Majda, Andrew J., Chen, Nan
Climate dynamics 2019 v.52 no.3-4 pp. 2351-2366
El Nino, climate, dynamic models, wind direction
The recent 2014–2016 period was marked by a failed El Niño favoring a subsequent extreme El Niño with dramatic worldwide impacts. Here this new type of major event so-called the delayed super El Niño is realistically captured by a simple dynamical model for the equatorial Pacific with emphasis on the role of state-dependent stochastic wind bursts. We analyze qualitative analogues for this event compared and contrasted with the 1997–1998 super El Niño in ensemble experiments based on the simple model. In agreement with recent studies, the timing and intensity of such an event is strongly controlled by atmospheric wind bursts, both easterly and westerly. In particular, the early stalling by easterly wind bursts and subsequent development by westerly wind bursts as observed during 2014–2016 is consistently retrieved. We show in addition that individual wind bursts may control the main characteristics of the event only during its early development while sequences of consecutive wind bursts have more important cumulative effects. Another important result from the present analysis is the significant statistical occurence of the delayed super El Niño (around 20–30%) compared with the one of directly formed super events as that of 1997–1998. Such a high occurence is directly linked to the random evolution of wind bursts and is retrieved here for all phases of the El Niño–Southern Oscillation used for the initiation of the ensemble experiments. These results suggest that the delayed super El Niño is not an unusual type of super event and could reoccur in the future.