STATISTICAL STUDY OF CLIMATIC JUMP IN THE REGIONAL ZONAL CIRCULATION OVER SOUTH-AMERICA

Using the climatic signal-noise ratio, as well as other tests, dates h ave been detected around which important changes in Northeasterly and Westerly circulation have been observed in mid-latitude South America. These changes in zonal circulation intensity which occur, on average, in periods of 10 years or more, have been generally coincident with t hose registered in the Northern Hemisphere, in the last century. The W esterly intensities series show climatic jumps along six months of the calendar year. Information on those registered in July of 1939, 1949, 1967 and 1977 and January 1974 is included. Climatic jumps were obser ved in Northeasterly intensities in the monthly and seasonal scales, r espectively, with no effect upon the annual values. An important chang e in average conditions of the North-easterlies detected at the beginn ing of the 1950s, and fluctuations of low frequency, might be the caus e of outstanding precipitation jumps in the Argentina's subtropical ar ea, where abundant (scanty) precipitation was associated with strong ( weak) Northeasterlies.