Temperature and precipitation conditions in Argentina associated with strong westerly mid-latitute

Abstract

This paper analyzes the incidence on temperature and precipitation of strong circulation from the west in the neighborhood of 45ºS. Circulation is estimated by a zonal index applied at 100º, 70º and 40ºW at 500 hPa and the strong circulation days by those which indices are smaller than the difference between the mean and the standard deviation of the daily indices from 1989 to 1998. When strong circulation from the west is calculated at 100º W, temperature anomalies over the country are positive in general and higher than 1ºC in southern Patagonia. Precipitation frequencies are greater than normal in southern Patagonia and the WNW of the country, and smaller in the remaining areas. Temperature anomalies are positive in practically the whole of Argentina and precipitation values greater than normal are practically confined to the south of 42ºS when the circulation from the west is more intense at 70ºW. For the same wind conditions at 40ºW, temperature anomalies are negative in Patagonia and positive in the NE and center of the country, while the greatest precipitation frequencies are found in most of the country except the western provinces. Temperature and precipitation values obtained under the analyzed conditions can be forecast with more than 69% probability when the index on 1 or 2 previous days was negative.