Relationship between values and trends of two circulation indices and temperature and rainfall in Argentina

Abstract

Extreme values of two circulation indices are examined for the time series covering the period 1960-2006. The influence of circulation on surface temperature and rainfall in Argentina is analysed using a zonal index Z and a meridional index R at the 1000 and 500 hPa levels. Seasonal means for all the years representing extreme negative values of R(Z) at 1000 and/or 500 hPa, determine mainly positive (negative) temperature anomalies with increased rainfall in both indices. These characteristics revert for extreme positive values of R(Z). At 1000 hPa, seasonal anomaly trends of R are negative and significant. Trends of Z are all positive and significant, except for winter when they are not significant. Signs of trends at 500 hPa are the same as at 1000 hPa, except for Z in winter and R in summer, whose values are not significant. Annual and seasonal trends of the anomalies of Z differences between 500 and 1000 hPa, are mostly negative, which implies a decrease in baroclinicity in southernmost South America. Analysis of the statistical values obtained for both variables generated by extreme values of R and Z, and of the signs and significance of index trends at 1000 hPa indicates that both circulation indices might contribute to surface temperature warming during the last years of the period 1960/2006. The increase in R, whose influence is greater than that of Z, might contribute to greater rainfall. © 2011 Royal Meteorological Society.