Mechanisms of the 2014-2016 Delayed Super El Niño Captured by Simple Dynamical Models

Recent studies suggest that atmospheric wind bursts in the tropical Pacific have played a major role during the 2014-2016 period marked by a failed El Niño favoring a subsequent super El Niño with dramatic worldwide impacts. Here we show that this new type of major event or so-called delayed super El Niño is realistically and easily captured by simple dynamical models with emphasis on the role of state-dependent stochastic wind bursts, both easterly and westerly. We analyze in particular 1) qualitative model surrogates for this event compared and contrasted with the 1997-1998 super El Niño, 2) their formation mechanisms and 3) statistical occurrence as generated by random wind bursts. Despite favorable ocean conditions atmospheric wind bursts differentiate the failure or development as well as the delay of El Niño events in the simple model. In particular, the early El Niño stalling by easterly wind bursts and subsequent development by westerly wind bursts observed during 2014-2016 is consistently retrieved along with a realistic spatial structure and chronology. The simple model further allows one to analyze El Niño ensemble statistics that reveals a significant occurrence of the delayed super El Niño Sulian Thual Department of Mathematics, and Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, NY 10012 USA E-mail: [email protected] Andrew J. Majda Department of Mathematics, and Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, NY 10012 USA, and Center for Prototype Climate Modeling, New York University Abu Dhabi, Saadiyat Island, Abu Dhabi, UAE. E-mail: [email protected] Nan Chen Department of Mathematics, and Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, NY 10012 USA E-mail: [email protected] (corresponding author) 2 Sulian Thual et al. type in addition to super events like the one of 1997-1998 and moderate events. The present theoretical findings therefore suggest that delayed super El Niño events are not necessarily unusual in the tropical Pacific despite not appearing in the recent observational record and could reoccur in the future.