DevelopmentsinEarthSurfaceProcesses ...

Climate and Geomorphologic-related Disasters in Latin America 11
precipitation mostly to the subtropical portions of the continent but occasionally
also into the tropical portions of the continent (Kousky 1979). Variability of the
SACZ also produces strong variability in the precipitation and wind patterns in
South America on intraseasonal timescales (Nieto-Ferreira et. al. 2003). On these
intraseasonal timescales, the Madden-Julian Oscillation causes 30- to 50-day oscillations
in precipitation and wind patterns in the eastern Amazon Basin and SACZ
regions during the austral summer (Carvalho et al. 2004) as well as in Central
America and the Caribbean during the boreal summer. On interannual timescales,
ENSO produces circulation and precipitation variability that affect most of Latin
America. On interdecadal timescales, the variability of rainfall in the drought-prone
Nordeste region of Brazil is strongly affected by the variability of SSTs in the
tropical Atlantic (Moura and Shukla 1981). The number of Atlantic ocean tropical
storms and tropical cyclones that affect Mexico is also affected by the interdecadal
variability of tropical Atlantic SSTs (Landsea and Gray 1992).
2.5. ENSO
The ENSO is a coupled ocean–atmosphere phenomenon that occurs in the
tropical Pacific Ocean and affects weather and climate all over the Earth. El
Niño episodes occur every two to seven years and are characterized by a
warming of the SSTs along the eastern tropical Pacific Ocean that occurs around
Christmas time, hence the name El Niño, or Christ Child in Spanish. El Niño
events last about 12 to 15 months, though sometimes El Niño conditions persist
for up to two years. La Niña events are characterized by warm SST anomalies in
the western tropical Pacific Ocean and cold SST anomalies in the eastern tropical
Pacific Ocean. Typical atmospheric conditions during El Niño events include
weakened trade wind easterlies over the equatorial Pacific, more rainfall than
normal in the eastern Pacific Ocean (Fig. 1.6) where SSTs are warmer than usual,
and less rainfall than normal in the western Pacific Ocean, Australia, and
Figure 1.6 Hurricane tracks in the Eastern Pacific and Atlantic oceans from 1851 to 2007.
Image courtesy of the National Hurricane Center^National Oceanic and Atmospheric
Administration (NOAA).