An Exceptionally Strong Easterly Wind Burst Stalling El Niño of 2014

Abstract:

Intraseasonal wind bursts in the tropical Pacific are believed to affect the evolution and major characteristics of El Niño events. In particular, the occurrence of two strong westerly wind bursts (WWBs) in the early 2014 pushed the ocean-atmosphere system towards El Niño – potentially an strong event by the end of 2014 according to climate models. However, the event’s progression quickly stalled, and the warming remained very weak throughout the year. Here we argue that the occurrence of an unusually strong basin-wide easterly wind burst (EWB) in June was a key factor that impeded the El Niño development. It is shortly after this easterly burst that all Niño indices fell rapidly to near-normal values, unable to fully recover later in the year. This easterly burst and the weakness of subsequent WWBs resulted in the persistence of two separate warming centers in the central and eastern equatorial Pacific, suppressing the positive Bjerknes feedback critical for El Niño. Eventually, only a weak warming developed stretching nearly uniformly along the equatorial Pacific. Experiments with a climate model with superimposed wind bursts support these conclusions, pointing to the importance of EWBs, which have received much less attention before than WWBs, for the development of El Niño events. Further, we discuss the role of these 2014 changes in the tropics for the development of El Niño in 2015.