Summertime Precipitation Variability over South America: Role of the Large-Scale Circulation

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Abstract
The observed large-scale circulation mechanisms associated with summertime precipitation variability over South America are investigated. Particular attention is paid to the Altiplano where a close relationship has been observed between rainfall and the position and intensity of the Bolivian high. Empirical orthogonal function (EOF), correlation, and composite analyses suggest that on intraseasonal timescales (typically 5–20 days), rainy periods on the Altiplano are associated with at least three types of circulation anomalies, involving either extratropical cyclones, cold-core lows, or the westward enhancement of the South Atlantic high. In each instance, the primary support for high rainfall rates is a moist, poleward flow at low levels along the eastern flank of the central Andes in association with the South Atlantic convergence zone (SACZ). The warm, low-level flow along the SACZ also inflates the overlying atmospheric column, resulting in an intensification and southward shift of the Bolivi... Abstract The observed large-scale circulation mechanisms associated with summertime precipitation variability over South America are investigated. Particular attention is paid to the Altiplano where a close relationship has been observed between rainfall and the position and intensity of the Bolivian high. Empirical orthogonal function (EOF), correlation, and composite analyses suggest that on intraseasonal timescales (typically 5–20 days), rainy periods on the Altiplano are associated with at least three types of circulation anomalies, involving either extratropical cyclones, cold-core lows, or the westward enhancement of the South Atlantic high. In each instance, the primary support for high rainfall rates is a moist, poleward flow at low levels along the eastern flank of the central Andes in association with the South Atlantic convergence zone (SACZ). The warm, low-level flow along the SACZ also inflates the overlying atmospheric column, resulting in an intensification and southward shift of the Bolivi...

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