Sea surface temperature in the north tropical Atlantic as a trigger for El Nino/Southern Oscillation events

Abstract

El Nino events, the warm phase of the El Nino/Southern Oscillation (ENSO), are known to affect other tropical ocean basins through teleconnections. Conversely, mounting evidence suggests that temperature variability in the Atlantic Ocean may also influence ENSO variability(1-5). Here we use reanalysis data and general circulation models to show that sea surface temperature anomalies in the north tropical Atlantic during the boreal spring can serve as a trigger for ENSO events. We identify a subtropical teleconnection in which spring warming in the north tropical Atlantic can induce a low-level cyclonic atmospheric flow over the eastern Pacific Ocean that in turn produces a low-level anticyclonic flow over the western Pacific during the following months. This flow generates easterly winds over the western equatorial Pacific that cool the equatorial Pacific and may trigger a La Nina event the following winter. In addition, El Nino events led by cold anomalies in the north tropical Atlantic tend to be warm-pool El Nino events, with a centre of action located in the central Pacific(6,7), rather than canonical El Nino events. We suggest that the identification of temperature anomalies in the north tropical Atlantic could help to forecast the development of different types of El Nino event.