The influence of South Atlantic and Pacific Highs over precipitation in Argentinean Buenos Aires Plain Region

ROLLA, ALFREDO; GONZÁLEZ, MARCELA HEBE

fortaleza

Congreso; Adaptation Future 2014: Third International Climatic Change adaptation Conference; 2014

CCST INPE

The relation between seasonal rainfall and the intensity and position of South Atlantic and Pacific Highs is analyzed. Precipitation in this region is affected by two main factors: the humidity advection from the north and Atlantic Ocean and by the front passages from the south. Both effects act simultaneously, however the first prevails in summer and the second in winter. 1000Hpa geopotential heights data derived from European Center Reanalysis (ECMWF) were used to detect Atlantic and Pacific High and to calculate the position and intensity of their centers. The mean values showed that both anticyclones displace towards the north in austral winter and towards the south in austral summer ant their intensity has a maximum in winter and early spring. However, a relevant position and intensity interannual variability was present. The position and intensity of both Southern Highs were correlated to seasonal precipitation in Buenos Aires. Results indicated that winter rainfall in Buenos Aires was favored when the South Atlantic High was more intense and displaced southern of its mean position showing that the Atlantic High is relevant to access humidity into the continent and this advection determines the rainfall increase. The relation between latitude and rainfall is strong in spring too. Meanwhile, summer and autumn rainfall was greater than normal when the South Atlantic High was weakened and displaced northern from its mean position because fronts can arrive to this region displacing over the continent. It is important to note that the interannual variability is caused mainly by interannual variability of humidity advection in winter but mainly by front frequency in summer. The South Pacific High acts regulating the position of storm tracks derived from Rossby waves displacing along the Pacific Ocean. When its position was related to Buenos Aires rainfall, results indicated that winter (summer) rainfall is favored by a weakened (stronger) high and when it is displaced northern (southern) and eastern (western) of its mean position, especially in central (northern) Buenos Aires.