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Satellite eyes focus on El Niño 
At the end of 1997, torrential rains battered California, mudslides struck in Peru - and many inhabitants of southern Canada saved up to 30% on their winter heating bills. The cause? El Niño, a huge temperature shift in the Pacific Ocean which spawns climate changes globally. El Niño is a regular event, and using satellite earth observation data, scientists are becoming able to predict its onset months in advance, and are beginning to understand the mechanisms which cause it. "In normal years, there's a large area of warm water in the western Pacific, and colder water at the eastern side. In El Niño years, that warm water shifts eastward, which has major effects on the atmosphere above the ocean, and thus the climate of nearby and distant countries," explains Joel Picaut, of France's Institut de Recherche pour le Développement.
"No one is yet quite sure of the precise mechanism that causes an El Niño," comments Picaut. "It's clear that the movement of the warm water and the change in the wind patterns are closely linked, but we do not yet know which is the cause and which the effect." The warm water in the west causes convection in the atmosphere and a relatively constant wind from east to west - the "trade winds". When the El Niño cycle begins, the trade winds reduce, no longer pushing water toward the warm pool, and the mass of warm water begins to flow eastward, toward the Galapagos Islands and the Ecuadorian and Peruvian coasts. "Over a period of 1-2 weeks, we see so-called 'westerly wind bursts', in which the direction of the trade winds reverses. At the equator, you see a very interesting effect, where the wind and the Earth's rotation combine to trigger "Kelvin waves", which are like a wall of water 30 cm high moving across the pacific at about 250 km per day. You can see the Kelvin waves clearly and monitor their progress using radar altimeter and in situ temperature data," says Picaut. These fast-moving Kelvin waves are the heralds of the more sedate progress of the main body of water, which sweeps from the Western Pacific at only 50km per day. "We don't yet know if the wind bursts and Kelvin waves are fundamental to the El Niño mechanism, or whether they are simply an effect on top of the underlying transfer of warm water from west to east," comments Picaut. Despite the mystery surrounding the origins and mechanism of El Niño, scientists are making significant strides in the ability to predict its onset. "Although El Niño is cyclical, it's not like clockwork, and the strength of the effect varies dramatically from one event to the next. We had a very strong El Niño in 1982/83, another in 86/87, a series of small ones in 91/92 and 93 and a huge one in 1997," comments Picaut. "In 1999/2000, we were actually in 'La Niña', which is the opposite effect." La Niña causes an increase in the trade winds, and more cooling of the waters around the Galapagos Islands.
Prediction may be an inexact science, but any warning is better than none at all. In the US, the prediction led to bulldozers moving in along the Californian coast to create better sea defences against the El Niño-charged Pacific rollers. With sufficient warning, countries like Ecuador and Peru, which will bear the brunt of rains 10-40 times heavier than normal, can prepare to deal with flooding by improving watercourses and moving people from the areas most threatened by flash floods and mudslides. "If you know El Niño is on the way, you can be ready," sums up Joel Picaut.
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El Niño animation sea surface temperatures (http://esamultimedia.esa.int/images/asst-mm_ani_me.mpeg)