Searching For El Nino

The chain of events leading to the unusual weather known as El Nino begins when the trade winds that usually blow across the Pacific from east to west diminish. As a result, the bulge of warm water that the winds keep bottled up near Indonesia slosh back toward South America. Through "teleconnections," this movement of warm water affects weather worldwide.

1 Normal year: The trade winds blow from east to west, pulling warm water behind. El Nino year: The trade winds slacken, for largely mysterious reasons.

2 Normal year: Cold, nutrient-rich water wells up from below, supporting the Pacific food chain. El Nino year: Stationary warm water prevents up-welling. Fish stocks fall.

3 Normal year: A pool of warm water sits off Indonesia, bringing rains to the region. El Nino year: The warm water sloshes east, taking the storm clouds with it.

4 Normal year: The jet streams deliver rain to southern Mexico and the Pacific Northwest. El Nino year: The jet streams shift north, and so do the rains.

Below the surface. In El Nino years, the thermocline--the depth where warm surface water meets cold deep water--drops in the east. The cold, nutrient-filled water cannot rise, starving plankton and hence fish.

THOMAS HAYDEN in New York, Donna Foote in Los Angeles AND BROOK LARMER IN MIAMI

© 1997