How the Atlantic multidecadal oscillation (AMO) modifies the ENSO influence on the South American rainfall

This article analyses the relations of the Atlantic multidecadal oscillation (AMO) and the El Nino-Southern Oscillation (ENSO) and their influence on the South American rainfall. The ENSO-related precipitation anomalous composites over South America show more (less) organized patterns with the significant anomalies occupying extensive (reduced) areas when ENSO and AMO are in the opposite (same) phase. The El Nino (La Nina) events in the cold (warm) AMO phase are, in general, stronger than those in the warm (cold) AMO phase. The strong El Nino (La Nina) events in the cold (warm) AMO phase are due to the presence of a negative (positive) inter-Pacific-Atlantic sea surface temperature (SST). The negative (positive) SST anomalies in the equatorial Atlantic reinforce the El Nino (La Nina) in the tropical Pacific through an anomalous Atlantic Walker circulation. In consequence, the ENSO-related precipitation anomalies over South America are more intense and with less horizontal structure under the existence of this connection between the climate variability of the tropical Atlantic and Pacific Oceans. As far as the authors know, the results presented here have not been discussed before and have important implications for regional climate monitoring, as well as for modelling studies. Copyright (c) 2013 Royal Meteorological Society