Evolving anomalous SST patterns leading to ENSO extremes: relations between the tropical Pacific and Atlantic Oceans and the influence on the South American rainfall

Abstract

AbstractSeveral studies have provided observational and numerical evidence that the tropical Pacific and Indian Oceans are influenced by the tropical Atlantic within a one season time scale. The influence of the Atlantic equatorial mode (AEM) in the Pacific El Niño‐Southern Oscillation (ENSO) mode is observationally re‐examined. The analyses focus on the ENSO‐related evolving sea surface temperature (SST) and sea level pressure (SLP) anomalies in the Tropics that follow the occurrences of AEM events and those that are independent of the AEM. The cold (warm) AEM followed by El Niño (La Niña) shows a sequence of maps that might be explained by the mechanism previously outlined on the relationship of the tropical Atlantic and the other tropical Oceans. This mechanism involves an anomalous Atlantic Walker circulation and a Gill–Matsuno‐type atmospheric response to anomalous cooling or warming in the tropical Atlantic. The seasonal timing of the relationship studied differs from that of the previous studies. Here, it is noted that the Atlantic SST anomalous conditions are persistent and might be noted 5–6 months before that proposed in previous results. Furthermore, the ENSO extreme conditions are reinforced and maintained by the east–west SST anomalous gradient in the tropical Pacific. Also, the precipitation composites over South America for the ENSO extremes, which are AEM‐dependent and AEM‐independent cases, are discussed. The AEM‐dependent ENSO extremes combine the effects from the tropical Pacific, and equatorial and tropical South Atlantic on the rainfall over South America. The results presented here, to the authors' knowledge, have not been discussed before and might represent a potential for long lead predictability of the climate variations in the tropical Pacific. Copyright © 2010 Royal Meteorological Society