In Ecuador or Peru the air and water are sometimes a bit warmer and the waves are a bit higher. When that happens, it means the area has been hit by a ?Kelvin wave,? which means an El Nino is on the way.
?Kelvin waves are warm bumps in the Pacific Ocean,? says JPL oceanographer Bill Patzert. They form around Indonesia and travel east toward the Americas.?
El Ni?os and Kelvin waves are both triggered by winds in the Pacific Ocean. Sometimes the trade winds slow down for a few days or weeks -- researchers aren?t sure why -- and warm water slides back across the Pacific toward the Americas. ?"That?s a Kelvin wave,? says Patzert.
El Ni?o begins when trade winds slow down for many months. Then, says Patzert, strong Kelvin waves cross the Pacific ?like a conveyor belt,? depositing warm water near South America where the ocean is normally cold. This new warm pool of water alters weather all over our planet. Rains that would normally hit the western Pacific shift toward the Americas, while places like Australia, Indonesia, and India become dry.
?El Ni?o can do a lot of damage? says Patzert, ?but it?s not all bad.? The last El Ni?o in 1997 suppressed Atlantic hurricanes, lowered winter heating bills in New England, and allowed surfers to use the suddenly warm beaches in California. There was extra sledding in the Sierra Nevada when it snowed in June.
However, Coastal villagers in South America fled the rains in 1997 that washed away their homes and brought record numbers of mosquitoes. Meanwhile, normally wet places like Australia and Indonesian were hit by terrible droughts and wildfires.
Farmers can profit from changing weather patterns by cultivating ?El Ni?o crops.? Rice and beans can be planted in areas normally too dry to support them. But this is only possible if growers know when an El Ni?o is coming.
Scientists have developed computer models that do a good job forecasting El Ni?o's effects, but only after an El Ni?o has begun. ?The hard part is predicting when El Ni?o will begin,? says David Adamec, a climate researcher at NASA.
The interval between El Ni?os varies from 3 to 7 years and researchers don?t know why. Because the last one began in 1997, the next could begin as early as this year or as late as 2004.
After the El Ni?o of 1982-83 took forecasters by surprise, the United States, Japan, and France strung 70 buoys across the equatorial Pacific to monitor water temperature to a depth of 500 meters, as well as winds, air temperature, and relative humidity. They are designed to be an early warning system for El Ni?o.
El Nino warnings also come from the US-French TOPEX/Poseidon satellite. It can measure the height of the ocean?s surface with radar. Warm water expands, so Kelvin waves appear as traveling bumps in the satellite?s sea surface elevation maps.
Both TAO and TOPEX/Poseidon have tracked the latest Kelvin wave since it formed near Indonesia in Dec. 2001. ?The wave crossed the Pacific in January and reached South America in February,? says Patzert. ?It looks a lot like one that crossed the Pacific in early 1997 -- just before the last El Ni?o.? But he says, ?Kelvin waves appear in the Pacific every winter; they don?t all mean El Ni?o is coming.?
Adamec says, ?It?s too soon to say. The real test will be what happens this spring.?
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El Ni?o, the periodic warming of Pacific Ocean waters that affects the weather worldwide, started about 6,000 years ago, according to a study of ancient fish bones.
Fish bones discarded about 6,000 years ago by ancient peoples in Peru show that ocean catfish lived in water that averaged six to seven degrees warmer than it is now and that there was little variation in the water temperature.
C. Fred T. Andrus of the University of Georgia says that if El Ni?o was occurring at the modern rate, one every two to seven years, then the bones from the fish would have reflected the temperature variation. ?We don?t see that,? he says. ?Our data strengthen the argument that El Ni?o, as we know it, began relatively recently - since about 6,000 years ago.?
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