GEOPHYSICAL MONOGRAPH SERIES, VOL. 186, PP. 149-162, 2009
Characteristics of Amazonian climate: Main features
This chapter summarizes our current knowledge on the mean climatological features of Amazonia. Significant uncertainties remain
in our understanding of the 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 of the South America Monsoon System
(SAMS). The SAMS is controlled by large-scale thermodynamic 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 of the
subsequent wet season. The 30- to 60-day oscillation is the major mode of intraseasonal variability. Interannual variability
of the hydroclimatic system is strongly related to El Niño-Southern Oscillation. More generally, tropical Pacific and Atlantic
SSTs control rainfall variability in Amazonia, and SW Atlantic 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 of rainfall anomalies over Amazonia, whether drier or wetter,
during the Last Glacial Maximum, and paleoclimate reconstructions still suffer from lack of data.
Citation: Nobre, C. A.,