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Warming up to an El Nino.

Warning up to an El Nino

It's not nice to fool Mother Nature, butthat doesn't mean she won't fool us. Six months ago, it seemed all bets were off on an El Nino-Southern Oscillation (ENSO) episode developing in 1986, even though model predictions and earlier measurements had suggested otherwise. The waters off South America's west coast had started to become warmer than normal in January 1986 -- one sign of a developing ENSO, in which unusually warm waters in the equatorial Pacific, accompanied by a low-pressure system over Indonesia and Australia and high pressures over the central Pacific, disrupt weather patterns worldwide. But the warming in that region never became very pronounced, and by the end of May it had ceased (SN: 6/7/86, p.357).

Then in August and September, someof the classic signs of an ENSO began to appear. Warmer-than-normal waters in the central Pacific began to spread eastward. An advisory issued Jan. 12, 1987, by the National Oceanic and Atmospheric Administration's Climate Analysis Center, states that rainfall, fueled by the warm waters, has been heavy in the central Pacific since November. At the same time, the Philippines, Indonesia and northern Australia have been drier than normal. Other ENSO signs are wetter-than-usual Gulf Coast states and warmer-than-normal conditions in the western United States and Canada.

"Some ENSO episodes start out with abang and are very strong from the beginning," says Vernon Kousky of the Climate Analysis Center in Camp Springs, Md. This one "started all very weakly, and it had most of us wondering whether it would evolve into a full ENSO or not," he says. "Each ENSO is different from the previous ones. We just have to learn with each one."

Compared with the 1982-83 ENSO,which led to the deaths of 1,100 people, killed vast numbers of sea life and caused $8 billion in damage, this one is very mild. Sea-surface temperatures in the central and eastern equatorial Pacific are now only about 1" to 2"C higher than normal, whereas temperatures in the eastern equatorial Pacific during the comparable stage of the 1982-83 episode were 4[deg.]C, and in some places 6[deg.]C, warmer than normal, according to Kousky.

If the greater-than-normal warming inthe eastern Pacific persists until temperatures reach their peak in March or April, he says, then Peru and Ecuador may be faced with increased rainfall, and warm waters could threaten those nations' fishing industries. "That's the part we don't know yet," he says. "It's very difficult to predict how the ENSO will evolve."

But forecasting capabilities are improving. InMarch of last year, Stephen E. Zebiak and his colleagues at the Lamont-Doherty Geological Observatory in Palsades, N.Y., using a coupled ocean-atmosphere computer model, predicted that a small to moderate ENSO would develop (SN:3/22/86, p.184). "The model predicted a warming earlier and somewhat larger than what has occurred," says Zebiak. "We also predicted that the [event] would get to its mature phase at the present time and die out by the middle of this year. Of course, we don't have the final word on the yet."

The current episode should helpZebiak and others to refine their models of the complex ocean-atmosphere dynamics that create ENSOs, because this one is better monitored than any other, with research vessels and an unprecedented number of ocean buoys, say Kousky. But until the computer model, and monitoring systems are perfected researchers can still take clues from a very nontechnical source -- the animal kingdom.

According to the National GeographicSociety of Washington, D.C., large numbers of Galapagos Island iguanas began breeding in September last year -- several months earlier than usual. The society reports that unusual breeding behavior last summer and fall of these and other species, including green sea turtles and finches, may indicate that the animals, many of which are highly sensitive to temperature changes, were anticipating bad weather brought on by an ENSO.
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Title Annotation:warmer-than-normal waters found in central Pacific Ocean
Author:Weisburd, Stefi
Publication:Science News
Date:Jan 24, 1987
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