Geoscience Reference
In-Depth Information
along with climate change? Two major events occurred at the end of
the last century and are imprinted in our minds: the event of 1982-
1983 and that of 1997-1998. El Niño plays a regulating role in energy
transfers on an almost global scale but we only have a limited history
of it and the coupled models used to study the climate and its
evolution can barely capture all its characteristics.
The other equatorial oceans are not exempt from variability. The
Atlantic Ocean shows an anomaly very similar to El Niño at the
Equator, but it has a much weaker amplitude and scarcely lasts a
season. However, it also shows a degree of variability over decades,
characterized by a 'seesawing' of the centers of pressure between
the southern hemisphere and the northern hemisphere. This large-scale
anomaly modulates the interhemispheric transfer through the trade
winds as well as the oceanic heat transport.
As for the Indian Ocean, it is marked by an anomaly called the
zonal south Indian Ocean Dipole. It is characterized by a warming in
the region to the north of Madagascar and a cooling to the west of
Australia. This oceanic situation accompanies winds from the east on
the Equator, which reverse the equatorial surface current toward the
west whereas in this ocean, the equilibrium situation is characterized
by the presence of eastward jets along the Equator (or Wyrtki jets),
well marked in the intermonsoon periods. This situation is associated
with a deficit in precipitation to the east of the Indian Ocean and
reinforcement to the west. This raises the question of whether this
anomaly, which presents as a mirror anomaly of El Niño, is
effectively linked to it. The answer is not simple since the Indian
Ocean was one of the first to warm and to modify its variability; it
seems that the links between its own variability and other external
sources such as El Niño have changed over the last century.
2.4.3.
Other types of variability
Climate change poses a challenge for its detection in ocean and
atmospheric environments. The long (and still very rare) observation
series that we have available show indeed that the climate is altering a
