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26.02.2008 17:30 Age: 12 yrs

Altimetry applications in video: El Niño

Category: Website updates

El Niño and La Niña are well-known climate events occurring in the tropical Pacific Ocean. On the eve of the launch of Jason-2, what more can we learn about these phenomena?

See El Niño video: flash (10 Mo) or mpeg (33 Mo)

El Niño and La Niña are the names of climate events occurring in the tropical Pacific Ocean, which are now globally infamous. They characterise a close relationship between the ocean and the atmosphere, in which the main protagonists can have devastating consequences worldwide.

In the beginning, there were the easterly trade winds. During a normal pattern, they push surface waters in the Pacific from east to west. In order to balance this movement, nutrient-rich cold waters well up to the surface at the eastern side of the basin, where they are the basis of an abundant ecosystem.

An unchanging picture? No! This balance is sometimes upset by weakening easterly trade winds or by another wind system, blowing contrary to the trade winds. For centuries, South American fishermen noticed sudden, periodic drops in their fishing catches, in connection with higher ocean temperatures. Often at a peak around Christmas, they named the phenomenon "El Niño" (Baby Jesus in Spanish). Heavy rains, drought, fires, and other extreme weather events follow it.

Then came La Niña, in which the opposite occurs. The easterly trade winds strengthen, and colder than normal temperatures are observed in the tropical Pacific. Other extreme weather events are connected with it.

Satellite altimetry, which measures  sea surface height (which rises with higher temperatures during El Niño or falls with colder temperatures during La Niña), is vital for the early detection, analysis and close monitoring of these phenomena. Topex/Poseidon was one of the first witnesses of the 1997-98 episode, which occurred with exceptional amplitude. Today, satellites and in situ observations have increased the available data and thus allow the numerical models to be refined. Three moderate El Niño episodes occurred in 2002, 2004 and 2006 but due to the complexity of ocean-atmosphere interactions, their intensity was not correctly forecasted. To tackle the fact that no real periodicity can yet be determined, and to determine the extent to which global warming affects this recurring phenomenon, Jason-2 will help by ensuring continuity of observations, and improving data quality.

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