Instraseasonal Easterly Wind Surges and the Onset of La Niña Events

Abstract:

Although warm El Niño-Southern Oscillation (ENSO) events, also called El Niño events, first caught the attention of the wider scientific community for their impacts on global seasonal weather anomalies, it is now widely recognized that cool-ENSO (La Niña) events, also drive socio-economically important anomalies. The importance of better understanding the effects and processes controlling the predictability and impacts of La Niña events rivals the importance of improving the understanding of these aspects of El Niño events. We show here that intraseasonal events of easterly wind stress in the western and central tropical Pacific play an important role in the onset and evolution of La Nina events. These easterly wind surge events are identified using reanalysis wind stress fields, validated against buoy measurements. Analysis of the observed changes in sea surface temperature following them in the 1986-2012 period, as well as experiments with easterly wind surge forcing of an ocean general circulation model, show that these easterly surges, whose frequency is a function of ENSO state, are able to affect La Nina events in a fashion analogous to their westerly wind event counterparts that have been shown to be important in the onset and evolution of El Nino events.