Diagnóstico y pronóstico de situaciones sinópticas conducentes a ciclogénesis sobre el este de Sudamérica

Abstract

One of the strongest cyclogenetic regions of the Southern Hemisphere is located between 20 and 35°S over the eastern part of the American continent and the adjacent Atlantic Ocean. Depressions are often associated with heavy rainfall and strong winds over Rio de la Plata causing frequent floods. This research deals with the mean synoptic conditions associated with Eastern South America cyclogenesis and eventual objective forecasting methods. The average maps of geopotential height at 1000 and 500 hPa levels and thickness at 500/1000 hPa were calculated up to 5 days in advance, using 54 cases. The perturbations in the middle troposphere causing these cyclones may be detected 5 days before onset of the low pressure system. The disturbances are cold; they intensify with height and move slowly at latitudes further north than usual. This suggests that cyclogenesis may be associated with cut-off lows. Surface disturbances move slowly towards the continent; they are interrupted as they cross the Andes and they regenerate at lower latitudes east of the Andes. Multivariate discriminant analysis was used to develop objective forecasting methods. The proposed forecast has a range of up 48 hours with high reliability. The major predictors are related to the intensity, length and location of the disturbances in the middle troposphere, the baroclinicity, the location of surface systems as referred to the Andes, and the zonal circulation index.