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El Niño: definition.
El Niņo events are large climate disturbances which are rooted in the tropical
Pacific Ocean, and occur every 3 to 7 years. They have a strong impact on the
continents around the tropical Pacific, and some climatic influence on half of
the planet. The developed phase of El Niņo is characterized by a temperature elevation
of a few degrees Celsius at the ocean surface (3 to 6° Celsius, 5 to 11° Fahrenheit),
from the coasts of Peru and Ecuador to the center of the equatorial Pacific Ocean.
A consequence of such warming is the long-term perturbation of the weather systems
over the lands around, notably heavy rains in usually dry areas, drought in normally
wet regions. El Niņo is also seen as the warm phase of the irregular climate oscillation
called ENSO (El Niņo/Southern Oscillation), which is caused by unstable interactions
of the ocean and atmosphere. Conversely to El Niņo, the cold phase, La Niņa, occurs
with some cooling of the surface waters in the equatorial Pacific Ocean. A La
Niņa event may follow an El Niņo, but not always.
Who cares? since El Niño (La Niña, ENSO) is the most intense
short-term perturbation of the Earth climate system, anyone dealing with climate
change has, at some point, to consider El Niño effects and mechanisms.
Consequences of large El Niños can amount to several $US billions, therefore
its routine prediction 6 to 24 months in advance fosters much interest from a
scientific point of view as well as from a social and economic perspectives.