Signals mount that a new El Niño is gathering steam

This longer-term change could account for the trend in stronger El Niños, which would have been nurtured in water already undergoing long-term warming. What isn't clear, the team notes, is whether this change is a result of global warming or natural variability. Records are too short, they say, to yield any clues.

Researchers also are becoming increasingly attuned to the importance of regional climate patterns that can mask or intensify El Niño's farflung effects.

Typically, forecasters expect increased rainfall in equatorial East Africa, drought in Southern Africa, and weak summer monsoons in India during an El Niño. In the 1997-98 episode, however, Kenya, Somalia, and Ethiopia got much more rain than expected. Lake Victoria's water level rose nearly two meters. Drought didn't materialize in Southern Africa, and India was drenched.

The key may lie in the Indian Ocean basin. In 1999, researchers at IRI and the University of Colorado at Boulder published studies showing the Indian Ocean to have its own El Niño-like cycle. The timing of the changes in the Pacific and Indian Oceans produced the unexpected effects.

The work has prompted calls to deploy a network of buoys similar to the Tau-Triton array, which stretches across the tropical Pacific. Such buoys, which gather atmospheric and oceanographic data, allow forecasters to monitor conditions and provide the long-term database researchers can use to tease out patterns and trends.

r E-mail: spottsp@csps.com

Late 1800s

Fishermen coin the name El Niño to refer to the periodic warm waters that appear off the coasts of Peru and Ecuador around Christmas.

1928

Sir Walter Gilbert describes the Southern Oscillation, the seesaw pattern of atmospheric pressure between the eastern and western Pacific Ocean.

1957

Scientists learn that El Niño affects the entire Pacific Ocean.

1969

Jacob Bjorknes, of the University of California, Los Angeles, links the Southern Oscillation to El Niño.

1975

Klaus Wyriki, of the University of Hawaii, establishes that an eastward flow of warm surface waters from the western Pacific causes sea surface temperatures to rise in the eastern Pacific.

1976

Researchers use a computer model to demonstrate that winds over the far western equatorial Pacific can cause sea surface temperature changes off Peru.

1982

A severe El Niño develops in an unexpected manner but its evolution is recorded in detail with newly deployed ocean buoys.

1985

Several nations launch the Tropical Ocean-Global Atmosphere (TOGA) program, a 10-year study of tropical oceans and the global atmosphere.

1986

Researchers design the first coupled model of ocean and atmosphere that accurately predicts an El Niño event in 1986.

1988

Researchers explain how the lag between a change in the winds and the response of the ocean influences termination of El Niño and the onset of La Niña.

1996-1997

The array of instruments monitoring the Pacific, plus coupled ocean-atmosphere models, enable scientists to warn the public of an impending El Niño.

r Source: National Oceanic and Atmospheric Administration, PMEL, TAO

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