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Understanding El Niño

Everybody wants to know what the weather is going to do each day -- and with good reason, considering the many destructive storms and tornadoes that have hit the U.S. recently. In 1997-1998, the weather effect known as El Niño has been a favorite topic of conversation, as it seems to have caused most of those weather woes. But just what is El Niño? It's a periodic disruption of the Pacific's climatic system.

Many places received extra rain in 1998.
Usually, trade winds blow west across the Pacific, causing warmer ocean waters to "pile up" in the west: near Indonesia, the sea's surface is actually about a foot and a half higher than it is near Ecuador. However, on a cyclical basis, the trade winds die down, disrupting this normal pattern. The warmer waters stay east, raising the water temperature, rather than migrating west. This changes atmospheric circulation and weather patterns around the globe -- what we call El Niño.

This El Niño has had some notable effects. Rainfall in southeast Asia was far below normal in 1997-1998, while rainfall along the Pacific coast of South America was much higher than normal. North America, Europe, and east Asia saw higher than normal temperatures. California was hard hit by El Niño storms. Elsewhere in the world, dry conditions fostered severe forest fires and ongoing haze conditions.

In Peru, one of the hardest-hit areas, torrential rains have triggered floods and mudslides, washing away homes, farms, bridges, and highways. Floods have even uprooted a cemetery in Trujillo, sending coffins floating down the street.

Marine mammals from whales to otters have been especially battered. They survive on prey that breeds in cool, nutrient-rich waters, and the changes in water temperatures have made it difficult for them to find food. In Peru, 180,000 sea lions once lived along the coast, but just 30,000 now remain. The rest have died or migrated in search of food.

On average, El Niño occurs every two to seven years. This El Niño is expected to last through May, with normal conditions returning this summer. The term "El Niño," which refers to the Christ child, was given to this weather pattern by Peruvian fishermen who noticed that warm currents arrived one year at Christmastime.

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