Resumo

ALESSANDRO, Adelia P.. Blocking action arround seventy degrees West in the South of South America. Meteorologica [online]. 2005, vol.30, n.1-2, pp.3-25. ISSN 1850-468X.

Blocking situations near 70ºW south of South America are characterised. Cases which initiate to the west and those to the east of the above- mentioned longitude are distinguished. Averaging all cases it is seen that the Atlantic high as well as the Pacific high is displaced to the south for the first and second group respectively. Four different models result from the Principal Component Analysis, three of which representing blocking situations over the south-eastern Pacific Ocean and one of the south-western Atlantic. The trajectory of those highs that commence to the west have a cuasi zonal orientation with a speed of 20 Km/h, meanwhile those that region to the east have a slight component to the north with a speed of 20.5 Km/h. The mean centre of the anticyclones has a geopotential height of 227.7 gpm. The associated temperature anomalies are negative over most of Argentina, excepting the extreme south and the northeast, for both groups. When the blocking high is to the west of 70ºW the anomalies are more negative over Patagonia and more positive over the north-eastern country. Precipitations in Patagonia are superior with blockings beginning to the east of 70ºW with respect to those that first appear to the west, with exception of Ushuaia (54.48ºS, 68.19ºO) station and north-eastern Argentina. The situation of February 2004 is described. This month has been selected because has an extreme low zonal circulation index, a high meridional index and a very high blocking index I with respect to southern summer, showing in the study area the presence of  several blocking systems to the south of South America. These systems are associated with a lack of N and NE winds giving extremely low precipitations over north-eastern Argentina. on the other hand high temperatures over Patagonia and low temperatures over north-eastern and central regions of Argentina are observed.

Palavras-chave : Bocking system; Southern Hemisphere; Precipitation; Temperature.

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