El Niño Variant Is Linked to Hurricanes in Atlantic

by Cornelia Dean, New York Times, July 2, 2009

Scientists have known for some time that El Niño, the warm spell that turns up every four or five years in the waters of the eastern Pacific Ocean, reduces hurricane activity in the Atlantic. But in a new study, researchers at the Georgia Institute of Technology have linked a variant of that pattern — periodic warming in the central Pacific — to more frequent hurricanes in the Atlantic, particularly on the Gulf Coast and in the Caribbean.

The researchers and scientists who have reviewed their work said it was too soon to say whether the warming pattern resulted from global climate change or simply had been undetected.

Scientists can detect warming in the central Pacific earlier than they can discern the development of El Niño, the researchers said, so the new finding may help improve forecasts for hurricane seasons over all.

In an El Niño year, warming of the eastern Pacific changes air flow patterns in the troposphere, the lowest portion of Earth’s atmosphere, so that one layer moves eastward and the other westward. Wind shear then develops over the Atlantic, inhibiting the ability of storms to turn into tight, powerful gyres.

But the warming patterns that occur in the central Pacific cause the wind shear phenomenon to shift well to the west, the researchers say, allowing Atlantic hurricanes to form relatively unimpeded.

Peter J. Webster, a professor of earth sciences at Georgia Tech and an author of the report, said the variant pattern was discovered in the 1980s by Japanese and Korean researchers, who dubbed it “modiki” El Niño. (Modiki is Japanese for “similar but different.”)

Dr. Webster said it might be difficult for researchers to determine whether the warming pattern was new because their observational record was relatively short and their climate models were imperfect.

Kerry Emanuel, a climate expert at the Massachusetts Institute of Technology, said the new work was impressive. But he added that he believed that the pattern “has been there all along, but we just didn’t see it.”

Link to article: http://www.nytimes.com/2009/07/03/science/earth/03hurricane.html