Relations between ENSO and the South Atlantic SST modes and their effects on the South American rainfall

Abstract This paper analyses the relations between the El Niño/Southern Oscillation (ENSO) mode in the tropical Pacific and the sea surface temperature (SST) modes in the South Atlantic for the 1900–2006 period. In the South Atlantic, two modes are analysed in more detail: the South Atlantic dipole (SAD) mode, with centres at (15°S, Greenwich longitude) and at (37.5°S, 25°W) and the southwestern South Atlantic (SWSA) mode, with centres at (30°S, 40°W) and at the southern midlatitudes. The ENSO and SAD modes are lagged or lead connected depending on the period of analysis. An El Niño (a La Niña) precedes by up to 6 months the establishment of a positive (negative) SAD mode during the 1920–1930 and 1940–1980 periods. Otherwise, a positive (negative) SAD mode precedes by up to 1 year the establishment of a La Niña (El Niño) during the 1975–2000 period. On the other hand, the SWSA is strongly driven by the ENSO. The effects of both the SAD and SWSA modes on the South American rainfall are also discussed on a seasonal basis. In general, the SAD (ENSO) mode has a weak influence on the ENSO‐related (SAD‐related) rainfall anomalies over South America. On the other hand, in general, the SWSA and ENSO modes have a combined effect on rainfall of the southern and southeastern regions of South America. A particularly important result of the present analysis for climate monitoring and forecasting purposes seems to be the changing relations between the SAD and ENSO modes. Copyright © 2012 Royal Meteorological Society