A model for super El Ninos

Super El Ninos, the strongest and most powerful of El Ninos, impact economies, societies, and ecosystems disproportionately. Despite their importance, we do not fully understand how super El Ninos develop their intensity and unique characteristics. Here, combining observational analyses with simple numerical simulations, we suggest that eastern Pacific intensified super El Ninos result from the interaction of an El Nino and a positive Indian Ocean Dipole. Further, we identify a self-limiting behavior inherent to El Nino Southern Oscillation (ENSO) dynamics. This behavior-a consequence of the atmospheric Kelvin wave response that develops to the east of ENSO's convective anomalies-dampens sea surface temperature (SST) variations in the eastern Pacific, thereby preventing super El Ninos from developing through tropical Pacific dynamics alone. Our model explains the features of the large 1972, 1982, and 1997 El Ninos; the large SST anomalies during the 2015 El Nino, however, were likely enhanced by strong decadal variability.