Magazine article Science News

Once Bashful El Nino Now Refuses to Go

Magazine article Science News

Once Bashful El Nino Now Refuses to Go

Article excerpt

It took a long time to show its face, but the El Nino warming that finally arrived last year and upset world weather has turned into a lingering guest, remaining in place far longer than expected, meteorologists with the National Weather Service reported last week.

El Ninos represent periodic blips in the global climate that develop when warm water from the western equatorial Pacific Ocean spreads eastward in concert with shifting patterns of atmospheric pressure called the Southern Oscillation. These so-called warm events alter typical weather patterns around much of the globe, bringing rains to some regions and droughts to others.

As early as 1989, some meteorologists reported seeing signs of a developing El Nino, but the real warming did not begin until late 1991, reaching full force in early 1992. The El Nino played a role in causing North America's mild winter last year and contributed to a severe drought plaguing southeast Africa, according to meteorologists at the weather service's Climate Analysis Center (CAC) in Camp Springs, Md.

By the middle of last year, a drop in sea-surface temperatures in the central Pacific and other weather changes appeared to herald the death of the El Nino. Both human forecasters and computer models called for normal or colder-than-normal conditions to develop in the equatorial Pacific by the end of 1992 (SN: 7/4/92, p. 5). But weak El Nino conditions continued throughout the year and then unexpectedly gained strength in December, says CAC's Vernon E. Kousky.

"It is fair to say that what was predicted by our model, by and large, was not correct:' says Tim P. Barnett, an oceanographer at the Scripps Institution of Oceanography in La Jolla, Calif. Barnett is one of several scientists attempting to forecast conditions in the Pacific using computer models. …

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