Publicações

This chapter summarizes our current knowledge on the mean climatological features ofAmazonia. Significant uncertainties remain in our understanding ofthe complex dynamics of climate and climate variability in that region, which are due, in part, to the lack of observational data. The strong seasonality of the rainfall and the relatively rapid transition between the wet and dry season associated with onset of the rainy season is related to the establishment M the South America Monsoon System (SAMS). The SAMS is controlled by large~scalethermodynamic conditions influenced by the near-equatorial sea surface temperature (SST). It has been suggested that land-surface dryness in the dry season is the main cause of the delay in the onset ofthe subsequent wet season. The 30- to 60-day oscillation is the major mode ofintraseasonal variability. Interannual variability ofthe hydroclimatic system is strongly related to El Niiio-Southern Oscillation. More generally, tropical Pacific and Atlantic SSTs control rainfall variability in Amazonia, and SWAtlantic SST anomalies influence the variability of the South Atlantic Convergence Zone (SACZ). Land surface-atmosphere interactions have been proposed as a possible dynamical mechanism for the unexplained variance at the annual and interannual timescales. At decadal and interdecadal timescales, rainfall variability is related to the Pacific Decadal Oscillation mainly over the southern portions, and linked to the North Atlantic Oscillation. At paleoclimate timescales, there is large uncertainty on major aspects of rainfall variability over tropical South America. For instance, there remains uncertainty on the basic character ofrainfall anomalies over Amazonia, whether drier or wetter, during the Last Glacial Maximum, and paleoclimate reconstructions still suffer from lack of data.