Tendências na temperatura da superfície do mar e precipitação na América do Sul sob aspectos relativos ao aquecimento global e à variabilidade de baixa frequência

Abstract

We investigated the trend in Sea Surface Temperature (SST) and precipitation over South America (SA) through the action of natural variations in different time scales, associated or not with anthropogenic variability. Long-term variability modes such as the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) and the interannual El Niño- Southern Oscillation (ENOS) mode play an important role in the global SST pattern and precipitation and their effects are felt across the globe. In the periods analyzed here, these modes undergo significant changes, which may play an important role in the context of possible changes in global SST patterns, in addition to the effect on climate caused by anthropogenic action. In the chapters shown here, we use Trend Empirical Orthogonal Functions (TEOF) analysis to determine trend patterns in three scenarios: i) long-term trends in precipitation over SA during the 1951-2016 period. In this case, long-term trends were evaluated, considering or not the ENSO effects; ii) trends in SST during the phase change of the AMO and PDO modes, analyzing the performance of these modes in defining precipitation patterns over the tropical sector of the SA, considering or not the effects of AMO and PDO separately; and iii) trends in SST during the AMO phase change, in this case analyzing the role of the AMO, associated with the global warming trend related to anthropogenic changes, in the characterization of ocean patterns, and implications on precipitation in the tropical sector of SA. In view of the results obtained, the main contributions include: i) in the presence of ENSO, SST variations in the equatorial Pacific intensify the Walker circulation, resulting from the configuration of the PDO, which modulates ENSO. This pattern configures a positive (negative) precipitation trend in Southeast SA – SESA – (tropical SA). Without ENSO, the Walker cell is driven by asymmetric warming of the Indian Ocean and Atlantic, which in turn sets up the increasing trend in northern SA and the weakening trend over SESA. Warming in the Indian Ocean and equatorial Pacific, associated with the seasonal component of SST, induce Rossby wavetrain patterns over the South Pacific to SA and modulate the circulation over SESA; ii) the total SST trend pattern is characterized by the combination of negative/positive phase xii of PDO/AMO. PDO accounts for most of the positive precipitation anomalies in the equatorial sector of SA, since, in its absence, the Walker cell is weakened and distorts the positive precipitation pattern. In turn, the AMO acts to prevent rain in the Brazilian northeast and to increase the regions with negative anomalies to the south of the study area; iii) The presence of AMO in the positive phase in the total SST pattern contributes to the characterization of the Pacific-Atlantic interbasin gradient. This configuration suggests a precipitation trend response since the interbasin gradient strengthens the Walker circulation, implying a positive (negative) rainfall trend over north (south) of tropical SA. Our results may have relevant implications for improving the climate understanding, monitoring and prediction.