Vorticity patterns for rainy and dry episodes in Argentina

Summary A synoptic climatological study of precipitation in some regions of Argentina based on 500-hPa relative vorticity fields derived from geopotential heights produced at the National Meteorological Service of Argentina is performed. Some climatic-synoptic inferences concerning the association between large and synoptic-scale behavior of the upper-level flow and the occurrence of precipitation at a given place through the construction of composite/biserial correlation fields are drawn. In general, the results indicate that the correlation between vorticity and precipitation is nearly null in the vicinity of each one of the stations examined, and becomes increasingly negative to the west (cyclonic circulation associated with precipitation), and increasingly positive to the east (anticyclonic circulation). Then, almost all region of Argentina is affected by the westerly wind regime with precipitation usually associated with cyclonic vorticity advection. However, each locality exhibits some proper features that condition the occurrence of precipitation as well as a marked regional variation. Geographical and seasonal inferences are highlighted. For central and eastern Argentina vorticity anomalies are well defined: cyclonic anomalies to the west and anticyclonic anomalies to the east, generally more significant to the west sector. For the subtropical northeastern region the inter-relationship between vorticity and precipitation is something smaller. The importance of cyclonic vorticity maxima increases southwards. The northwestern region fits a different spatial configuration of maxima and minima vorticity with the anomaly axis in the north–south direction as a consequence of the deep alterations of the synoptic-scale systems induced by the Andes. For moderate to heavy precipitation the dynamics of the midtroposphere is still a decisive factor in all of the regions of Argentina. It is emphasized that the vorticity anomaly patterns as a manifestation of large and synoptic-scale upper-level circulation capture a considerable amount of information that allows us to classify precipitation data.