El Niño and La Niña:
Tracing the Dance of Ocean and Atmosphere

By now most people have heard of El Niño, if only to know the name refers to some kinds of abnormal weather. The definition of "abnormal" varies widely with geography, though. For people who live in Indonesia, Australia, or southeastern Africa, El Niño can mean severe droughts and deadly forest fires. Ecuadorians, Peruvians, or Californians, on the other hand, associate it with lashing rainstorms that can trigger devastating floods and mudslides. Severe El Niño events have resulted in a few thousand deaths worldwide, left thousands of people homeless, and caused billions of dollars in damage. Yet residents on the northeastern seaboard of the United States can credit El Niño with milder-than-normal winters (and lower heating bills) and relatively benign hurricane seasons.

Originally, the name El Niño (Spanish for "the Christ child") was coined in the late 1800s by fishermen along the coast of Peru to refer to a seasonal invasion of warm southward ocean current that displaced the north-flowing cold current in which they normally fished; typically this would happen around Christmas. Today, the term no longer refers to the local seasonal current shift but to part of a phenomenon known as El Niño-Southern Oscillation (ENSO), a continual but irregular cycle of shifts in ocean and atmospheric conditions that affect the globe. El Niño has come to refer to the more pronounced weather effects associated with anomalously warm sea surface temperatures interacting with the air above it in the eastern and central Pacific Ocean. Its counterpart--effects associated with colder-than-usual sea surface temperatures in the region--was labeled "La Niña" (or "little girl") as recently as 1985.

The shift from El Niño conditions to La Niña and back again takes about four years. Understanding this irregular oscillation and its consequences for global climate has become possible only in recent decades as scientists began to unravel the intricate relationship between ocean and atmosphere. Although meteorologists have long been forecasting daily weather based on atmospheric measurements taken around the world, they had relatively little information about conditions in many parts of the world's oceans until the advent of arrays of fixed unmanned midocean buoys in the Pacific Ocean and orbiting satellites.

But technological advances were not the only key. As the following article recounts, atmospheric and oceanographic researchers, after years of independent inquiry into the basic workings of air and sea, at last joined forces. An elegant synthesis of these two fields of research now enables climatologists and oceanographers to construct theoretical models to simulate and predict the broad climate changes associated with ENSO. For example, scientists can now warn vulnerable populations of an impending El Niño event several months in advance, providing precious time in which to take steps to mitigate its worst effects. Invaluable as this prediction of El Niño is, it is just the first step toward the much longer-term goal of providing the climatic counterpart to the daily weather prediction that we have come to take for granted.

Flooded area in Lakeport, California as a result of the 1998 El Nino event. (Federal Emergency Management Agency)

Bush fire in Australia as a result of the 1998 El Niño event. (Photo courtesy of Fred Hoogervirst/Panos Picture/London)

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