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El Nino
| Article
# : |
12129 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
12 / 1987 |
2,499 Words |
| Author
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Michael H. Glantz
Michael H. Glantz is head of the Environmental and
Societal Impacts Group at the National Center for Atmospheric
Research (NCAR) in Boulder, Colorado. |
In the past few years newspaper headlines have been filed with stories about "severe," "bizarre," "crazy," "extreme," and "anomalous" weather patterns that have disrupted human activities in many parts of the world and caused devastation to life and property on a local, national, and regional scale. Much of this unusual weather--and even a minute slowing of the earth's rotation--has been blamed on an oceanic-atmospheric phenomenon known as El Nino.
El Nino can be defined as an invasion of warm surface water from the western part of the equatorial Pacific into the normally cooler waters of the eastern part of the Pacific Basin off the western coast of South America-mainly Peru and Ecuador.
The warm water heats the air above it, and if the right conditions exist, the water vapor condenses and forms clouds. Heavy rains then fall over normally dry areas, and as this warm mass of air eventually moves out of the region, sinking in the western Pacific, it inhibits rain in this usually wet area. Many atmospheric scientists believe that the air currents set in motion during an El Nino event move not only to the western Pacific, but also to remote regions outside the tropics to influence weather elsewhere.
Although El Nino originally referred to local conditions off the coast of Peru and Ecuador, the use of the term has been broadened by many scientists to represent all surface temperature warmings in the eastern and central Pacific. This trend typically begins around Christmas, and hence the name El Nino, Spanish for the Christ child, was coined by Peruvian fishermen.
The eastern equatorial Pacific is usually dominated by coastal upwelling--the upsurge of deep, nutrient-rich cold water to the ocean's surface. Such waters provide excellent breeding grounds for various levels of the food chain from phytoplankton to anchovies. Every Christmas season the winds that blow along the coast from the southeast slacken, the strength of the upwelling weakens, and the surface waters begin to warm. This trend usually lasts for a few months and by March or so the strong upwelling resumes again. Occasionally, however, the warm water continues to accumulate in the eastern and central equatorial Pacific, resulting in a large pool of warm water.
This pool is associated with sharply reduced catches off the coast of Peru and with destructive rains that occur in normally dry areas of Peru and Chile. It is also associated with the development of drought
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