Impactos na precipitação da América do Sul associados a AMO, PDO e aquecimento dos Oceanos

Abstract

Recent studies show changes in the variability of occurrence, with a tendency to increase rainfall and the hydrological cycle over the Amazon basin in recent decades. However, its causes are still discussed. Results from previous work demonstrated that warming of the tropical Atlantic triggered changes in the Walker circulation leading to an increase in the frequency and intensity of extreme floods in the Amazon. Concluding that despite the contribution of SST changes in different ocean basins (Pacific, Atlantic and Indian Oceans), the Atlantic Ocean contributed more than 60% of the total changes in contributions while the Pacific Ocean contributed in a secondary way. However, it has not been investigated how much such an increase in the change in the rainy season over the Amazon is associated with natural variations, such as the AMO and PDO oscillations or with warming in the Atlantic and Pacific oceans due to Global Climate Change. Therefore, this work's main objective is to investigate which climatic factors are associated with recent changes in the Amazon's hydrological cycle in recent decades (1979-2012). As a tool for carrying out this work, sensitivity experiments were carried out in which the changes observed in SST are imposed in different ocean basins. For the validation results of the Community Atmospheric Model version 5.3 (CAM5), it showed that it represented the climatological positioning of the Intertropical Convergence Zone (ITCZ) throughout all quarters and also the configuration of the South American Convergence Zone in the months of DJF and MAM. Regarding the model's sensitivity to the AMO, PDO and linear trend signals, a reduction in rainfall was noted over the Northeast during the DJF and MAM seasons in response to the AMO, and an increase in precipitation over the north of the Amazon. In the AMO_TEND experiment, there was a slight reduction in the maximum and minimum revisions. Associated with PDO, it was shown that this result occurred in the increase in the rainy season in the Amazon. On the other hand, when the linear trend was added to the experiments (PDO_TEND) a small increase in occurrences was observed over the Northeast of Brazil, caused by negative SST values over the South Topic Atlantic near the Northeast coast. Regarding the components of the atmospheric water balance, the AMO and PDO experiments show changes in surface runoff consistent with the introduction, mainly in the MAM quarter. The results of this study indicate that both the AMO and the DOP acted in the same direction to modulate the rainfall pattern over the western Amazon. On the other hand, except for a small change in intensity, the patterns of variations are not altered when considering the combination of SST variation associated with the low frequency oscillation (AMO or PDO) and warming due to Global Climate Change.