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1. Dysfunction in the ocean–atmosphere couple
Atmospheric convergence above the
warm waters of the Pacific during the
development of an ENSO (El Niño and
Southern Oscillation) event.
The trade winds in the Pacific Ocean usually push the warm waters
westwards, towards the North of Australia and Indonesia. On the other
side, along the coast of South America, these winds pull cold water from
the depths, dragging an upsurge towards the surface. However, every
three to eight years, the trade winds lose strength and the movement
goes into reverse: a huge reservoir of warm water, with surface area
equivalent to that of the North-American continent, then shifts
from the western Pacific towards the East and covers the cold
Australia
waters lying along the South-American coastline.
América del Sur
Thermoc
lina
The Latin-American coasts are then bathed by these warm waters. These evaporate,
causing frequent rainfall, even in regions that are usually desert. The most powerful
El Niño events correspond to a rise in temperature of about 4°C. These violent effects have
marked impact on marine life and the local climate, and also generate climatic disturbances at global scale.
After the CNES
2. El Niño - La Niña : from one extreme to the other
The El Niño event is the warm phase of a natural oscillation. Its cold-phase counterpart is
La Niña. This oceanic oscillation is coupled by an oscillation of the atmospheric pressure
between the western and eastern sides of the Pacific, to form the ENSO event. La Niña
has the opposite effect to El Niño: it brings cold and dry episodes, where its counterpart
results in heat and humidity.
ENSO involves water and energy transfer processes at the Equator. It is the
strongest manifestation of the climate natural variability.
owing
a Desert in northern Chile, foll
Flowers spring up in the Atacam
arkable
ed by El Niño episodes: a rem
unusual spells of rainfall provok
sierto florido”.
show of flowering known as “De
Satellite image of El Niño, 2009-2010
3. Can El Niño be predicted?
Scientists use in situ measurements and satellite data to unravel
15,0
and model El Niño for prediction of the onset of events and
9,0
scientists can predict the event 10 months in advance.
Centimeters
anticipate their impact at regional and planetary scale. Currently,
3,0
-3,0
When an El Niño event occurs, the
movement of huge masses of warm
water along the Equator towards the
East can generate a sea-level rise of over
15 cm. This shows El Niño as viewed by
the altimetric satellite Jason 1 in 2010.
-9,0
-15,0
140 °
130 °
120 °
©NASA, 2010