The role of oceanic feedbacks in the 2014–2016 El Niño events as derived from ocean reanalysis data

Abstract

Why did the predicted “super El Nino” fade out in the summer 2014 and the following year develop into one of the three strongest El Nino on record? Although some hypotheses have been proposed in previous studies, the quantitative contribution of oceanic processes to these events remains unclear. We investigated the role of various oceanic feedbacks, especially in response to intra-seasonal westerly wind busts, in the evolution of the 2014–2016 El Nino events, through a detailed heat budget analysis using high temporal resolution Estimating the Circulation and Climate of the Ocean—Phase II (ECCO2) simulation outputs and satellite-based observations. Results show that the Ekman feedback and zonal advective feedback were the two dominant oceanic processes in the developing phase of the warm event in the spring of 2014 and its decay in June. In the 2015–2016 super El Nino event, the zonal advective feedback and thermocline feedback played a significant role in the eastern Pacific warming. Moreover, the thermocline feedback tended to weaken in the central Pacific where the zonal advection feedback became the dominant positive feedback.