South American atmospheric circulation anomalies related to droughts in the northwest of Argentina (1951-1980)

M.E BOBBA, J. L. MINETTI

Abstract

 Based on a regional drought index carried out by other authors (Minetti et al., 2004), it has been possible to associate droughts with atmospheric pressure anomalies in South America. We attempted to group the fields of atmospheric pressure anomalies, which show circulation changes, with these drought indexes. We applied Lund’s methodology based on a monthly, seasonal and annual scale. It has been possible to select a small number of severe droughts related to circulation. Consequently, we conclude that some severe droughts are associated with the factors listed below. The main circulation alterations related to droughts describe in most cases the following: a) significant mountain range gradients, in this case we include the one that intensifies the western zonal flow (west-east) over Patagonia, which generates an anticyclogenesis on the Pacific Ocean coast and a cyclogenesis on the continent, b) anticyclonic subsidence, c) weakness of the north humid flow due to a diminution of the gradient between the Atlantic Ocean anticyclone and the continental depression and/or subsidence associated with the flow coming from this direction.

Keywords

Drought, atmospheric pressure anomaly, circulation

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