Relação entre oscilação decadal do pacífico, el niño-oscilação sul e a circulação atmosférica de verão na América do Sul

Abstract

The Pacific Ocean climate variability was analyzed in decadal and interannual scales in order to understand the interaction of it with the Atlantic Ocean and South America during the southern hemisphere summertime. For the analysis, monthly means of different meteorological variables were used for the time period from 1948 to 1999, corresponding to the Pacific Decadal Oscillation (PDO) phases. At the beginning an appropriate index (IDP), describing the decadal and interannual variability, was created, such way that its correlation with other climate indexes, just as SOI and PDO, resulted in coefficients above 0.5 and correlation coefficients between IDP and sea surface temperatures anomalies (SST) were above 0.3. Through events analysis, it was shown that the IDP is a satisfactory representer of interannual events subjected to the decadal variability, like ENSO, specially of moderate and strong events. IDP absolute values over 1 during the southern hemisphere summertime were selected. It was noticed that positive events were related to El Niño occurrence, and negative events to La Niña. They were all analyzed and grouped according to the PDO phases. (cold phase – 1948 to 1976; warm phase – 1977 to 1999). The results showed that, during the cold phase, more La Niña events have occurred but not as strong as the El Niños, however, during the warm phase, events of El Niño have greater intensity during the warm phase and La Niña events are fewer in number and greater in intensity. El Niños occurrences during PDO cold phase and warm phase La Niñas, although in a smaller number, results in greater impacts over South America summer circulation, especially regarding to the Bolivian High positioning, the Northeastern trough and the Intertropical Convergence Zone.