Contrasting Intraseasonal Variations of the Equatorial Pacific Ocean Between the 1997–1998 and 2015–2016 El Niño Events

Abstract

Abstract Oceanic intraseasonal variability (ISV) plays a vital role in the initiation and development of El Niño events. Mooring observations reveal contrasting characteristics of upper‐ocean zonal current ISV during different El Niño events. Compared to the 1997–1998 event, ISV of the 2015–2016 event was significantly weaker (by around 30–50%) over the equatorial Pacific basin, and the variability maximum was shifted to the east (~160°E). These differences can be largely explained by wind forcing features. ISV of surface winds in 2015 is overall weaker than in 1997. Intraseasonal westerly wind bursts in 1997 occurred near the western boundary and originated from the Indian Ocean, whereas in 2015, perturbations were mainly propagated from the northeast Pacific and achieved the peak power at ~160°E of the equator. These changes are likely associated with the decadal warming of the northeast subtropical Pacific and weakening of the Indian Ocean intraseasonal oscillation.