Atmospheric processes associated with dry and wet events in the Argentinean Pampas

Drought and flooding are recurrent weather phenomena that affect agricultural and water-dependent economies of the Argentinean Pampas. The evolution of monthly mean precipitation data from 1976 to 1997, treated as an areal mean series of the Standardized Precipitation Index (SPI) over the region, supports the selection of wet and dry events. According to the rainfall regime, two seasons are recognized: one wet (October to April) and another dry ( May to September), giving rise to dry/wet events in the wet/dry season. The NCAR-NCEP Reanalysis series of areal mean precipitation over the region shows some discrepancies when compared with the observed data series.

Analysis of the vertically integrated flux of water vapor and tropospheric circulation anomalies are performed in order to understand the causes of wet/dry events. Composites of the stationary and transient moisture flux based on NCAR-NCEP Reanalysis products suggests that more than one flow patterns could be related to each seasonal type of event. Dry events during the dry season are well represented by a stationary moisture flux divergence pattern, while wet events may occur with convergence in the stationary or transient flow.