Synoptic-scale circulation influence on the precipitation annual cycle in Southeastern South America.

BETTOLLI, MARIA LAURA; BARRUCAND, MARIANA; VARGAS, WALTER M

Conferencia; 10th International Conference on Southern Hemisphere Meteorology and Oceanography,; 2012

American Meteorological Society

A dominant feature of the climate of the Southeastern South America region (SSAR) is a precipitation annual cycle that shows a double maximum and abundant rainfall throughout the whole year. Studies involving the climate of the region often tend to describe the characteristic shape of this regime. However, they have not dealt with the the causes that determine it. In this context, the aim of this work is to explain the shape of the precipitation annual cycle in terms of the synoptic climatology, with the intent to analyze if it responds to changes in the intensity of the precipitation associated with a daily circulation pattern or changes in the frequency of a specific circulation pattern. Daily anomalies of 500 hPa geopotential height fields from the NCEP Reanalysis 2 were used to represent observed mid-level circulation for the period 1979-2008 in the spatial domain from 15ºS to 60ºS and from 30ºW to 90ºW. Cluster Analysis was performed together with Principal Component Analysis to determine the synoptic-scale circulation patterns. The optimal number of circulation types (CTs) was established in 10 groups by the pseudo-F statistic. The contribution of the precipitation during a specific CT to the total precipitation over the entire 30-year period, the occurrence of rainy days per CT and the daily intensity of precipitation per CT were used to analyze spatial and temporal precipitation variability. Daily precipitation data from two stations of SSAR were used in the analysis: Corrientes Aero (27°27? S, 58°46? W) and Ezeiza Aero (34°49?S, 58°32? W). The CTs identified can discriminate between dry and rainy day frequencies, and can also be related to a range of daily rainfall intensities. Results suggest that there are changes in the frequencies of the CTs associated with rainfall during the months of maximum precipitation.