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Missing winds may foil 2014's El Nino: rainstorms needed on West Coast will probably be unimpressive.

California won't see hoped-for relief from drought this winter, scientists say, because El Nino is likely to be weak or nonexistent.

Earlier this year, many scientists anticipated a blockbuster 2014 El Nino that would rival the record-setting 1997 event. That year's El Nino--a climate disruption generated by unusually warm seawater in the eastern Pacific Ocean--triggered severe weather worldwide, including storms and floods on the West Coast and droughts in Southeast Asia.

But now the Climate Prediction Center of the National Oceanic and Atmospheric Administration projects that a strong El Nino is unlikely and the chances of even a mild one forming have dwindled to about 60 percent.

A lack of wind gusts over the Pacific Ocean left this year's El Nino dead in the water, researchers propose September 26 in Geophysical Research Letters. Scientists think these winds push warm seawater eastward. The warm seawater in turn rises to the ocean surface along South America's coast and heats the atmosphere, causing dramatic shifts in weather.

"If we had the same series of wind events in 2014 as we had in 1997, we would have gone strongly toward an El Nino state," says study coauthor Jerome Vialard, a climate scientist at the Institut Pierre Simon Laplace in Paris.

An oblong pool of warm seawater more than 14,000 kilometers wide always blankets the West Pacific. During the first few months of both 1997 and 2014, this warm pool shifted east as the westward trade winds slackened.

The similarities between the two periods "set off an alarm within the community," says study coauthor Christophe Menkes, a climate scientist at the Institute of Research for Development in New Caledonia, a self-governing French territory in the southwestern Pacific. However, in July 2014, unlike in 1997, the warm pool in the Pacific swung back to its normal position before it could rise to the ocean surface, decreasing the chance of a full-blown El Nino.

Menkes believes El Nino conditions fell flat this year because wind gusts called antitrade winds stopped blowing in April. These eastward gusts, Menkes says, would have helped lock the warm pool in place after it shifted into the East Pacific.

To determine whether the missing gusts were the key difference between the 1997 and 2014 seasons, Menkes, Vialard and colleagues did a virtual wind swap. Using computer simulations of the Pacific, the team calculated how 2014 El Nino conditions would have progressed under the wind patterns observed in 1997.

The warm pool would probably have stayed in the east and not have retreated westward, the team found, significantly boosting the possibility of a strong 2014 El Nino event. The results indicate that if the antitrade winds don't return, Vialard says, "this year's El Nino is more or less dead."

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That's bad news for the West Coast. California is in the midst of one of the most severe multiyear droughts on record and multiple large wildfires raged across the state this summer. Many had hoped El Nino would bring much-needed water to the region, which has received only 55 percent of normal precipitation so far this year.

The root cause of this year's El Nino dud remains unknown, says Michelle L'Heureux, a NOAA climate scientist in College Park, Md. "The big question is why the winds weren't as strong and rigorous as they were in 1997," she says. Winds are difficult to forecast, L'Heureux explains, making El Nino events difficult to predict.

The uncertainty in part stems from the winds being influenced by atmospheric and oceanic conditions elsewhere on Earth, says climate scientist Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colo. The presence or absence of antitrade winds, he says, may be a by-product of the overall atmospheric changes that prompt El Nino as much as they are a cause.

Caption: Lukewarm Warm water in the Pacific Ocean sloshed eastward this spring, prompting many scientists to expect a strong 2014 El Nino like the record-setting one in 1997. Sea surface height is an indicator of how much heat is stored in the ocean; above-average heights (red) correspond with warmer-than-normal sea temperatures.
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Title Annotation:News: EARTH & ENVIRONMENT
Author:Sumner, Thomas
Publication:Science News
Geographic Code:1USA
Date:Nov 1, 2014
Words:684
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