Spring persistence, transition, and resurgence of El Nino

Abstract

We present a systematic exploration of differences in the spatiotemporal sea surface temperature (SST) evolution along the equatorial Pacific among observed El Nino events. This inter-El Nino variability is captured by two leading orthogonal modes, which explain more than 60% of the interevent variance. The first mode illustrates the extent to which warm SST anomalies (SSTAs) in the eastern tropical Pacific (EP) persist into the boreal spring after the peak of El Nino. Our analysis suggests that a strong El Nino event tends to persist into the boreal spring in the EP, whereas a weak El Nino favors a rapid development of cold SSTAs in the EP shortly after its peak. The second mode captures the transition and resurgence of El Nino in the following year. An early-onset El Nino tends to favor a transition to La Nina, whereas a late-onset El Nino tends to persist long enough to produce another El Nino event. The spatiotemporal evolution of several El Nino events during 1949-2013 can be efficiently summarized in terms of these two modes, which are not mutually exclusive, but exhibit distinctive coupled atmosphere-ocean dynamics.