Westerly Wind Bursts, El Nino Diversity, and the Warm Event of 2014

Abstract:

Each El Nino event is unique. The still developing event of 2014 is not an exception – its evolution has already surprised many researchers who in May anticipated a likely development of a strong warm event perhaps analogous to that in 1997/1998; however, by June - July its development nearly stalled. Whether one should still expect a strong warm event is now much less certain. It is believed that the activity of westerly wind bursts (WWBs) that occur in the tropical Pacific and the varying response of the coupled system to those bursts are among the key reasons for such uncertainty and, in general, of the broad diversity of El Niño events. For instance, WWBs that occurred at the beginning of 1997 and 2014 were favorable for the potential El Nino development. However, in the latter case the subsequent ocean-atmosphere interactions, which involve the interplay between the warm pool changes in the western/central Pacific and the warming of the eastern equatorial Pacific, might have impeded further development. In this study, we consider the evolution of different El Niño events after strong westerly wind bursts in a comprehensive coupled climate model and in the observations, aiming to find analogues to the event of 2014 and several other significant events and determine critical elements, and precursors, that affected their evolution, thus contributing to El Nino diversity.