ENSO-related rainfall anomalies in South America and associated circulation features during warm and cold Pacific decadal oscillation regimes

Abstract

El Nino/Southern Oscillation (ENSO)-related patterns of monthly reanalyzed upper-level circulation data and monthly rainfall time series over South America are revised for the 1948–1999 period considering the phases of the Pacific inter-Decadal Oscillation (PDO). The El Nino (EN) related composites show differences relative to the PDO phases as well as seasonal differences. EN signals in the South American rainfall are more conspicuous for the warm PDO (WPDO) regime, when seasonal differences are more pronounced, than for the cold PDO (CPDO). Differences for the 200-hPa stream function composites seem to determine the precipitation composite differences. In fact, the negative precipitation anomalies over northeast Brazil and the excessive rainfall to the south are explained respectively by a cyclonic center over eastern and northeastern Brazil and a weak anticyclonic center over southeastern South America for the WPDO regime. Positive precipitation anomalies over southeastern South America are located in a southern position for the CPDO regime when compared to those for the WPDO regime. These anomalies might be related to a strengthened upper-level subtropical jet stream associated with strong cyclonic circulation extending over southern South America for the CPDO regime. With regard to the linear and nonlinear parts of the precipitation anomaly patterns related to the ENSO, the nonlinear component is considerably smaller than the linear component, in particular, over northern and southeastern South America. This suggests that the linear approach of the South American precipitation response to the ENSO seems to be appropriated. Copyright © 2005 Royal Meteorological Society.