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Intense winter lightning zaps Gulf Stream.

Intense winter lightning zaps Gulf Stream

Meteorologists, like most people, tend to view lightning and thunderstorms as summertime phenomena powered by the sun's warning influence on the land surface. To their surprise, atmospheric scientists have discovered intense winter lightning over the warm waters of the Gulf Stream.

During early 1986, a network of lightning detectors recorded a high number of cloud-to-ground flashes off the coast of the Carolinas, reports Richard E. Orville of the State University of New York at Albany. Over a two-month period in winter, one ocean region experienced an average of seven flashes per 10 square kilometers. For comparisons, it typically takes an entire year for an area of similar size in upstate New York to accumulate the same number of flashes, Orville notes in the May GEOPHYSICAL RESEARCH LETTERS.

His work combines data from the detection network with information gathered during a 1986 experiment studying winter storms that develop off the East Coast. Orville found the most lightning-intense regions about 250 to 300 km offshore in the vicinity of the warmest sea-surface temperatures (about 20 [degrees] C). the lightning activity spread across the width of the Gulf Stream.

Until the 1986 winter storm experiment, scientists did not realize that warm water could generate strong convection of air currents, much like the convection driven by the sun-baked land surface during summer, according to Peter V. Hobbs of the University of Washington in Seattle. In restrospect, Hobbs says, it makes sense that the heat from the Gulf Stream could cause air to rise and thereby trigger thunderstorms and lightning.

Other ocean areas with warm currents may also experience winter lightning, and these regions could pose a hazard to passing aircraft and ships, says Hobbs.

Violent thunderstorms over the Gulf Stream may account for nautical legends about the area, Hobbs adds. "Going back to the days of sailing ships, the region off Cape Hatteras [N.C.] has been known as graveyard for ships," he says.
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Author:Monastersky, Richard
Publication:Science News
Date:Jun 2, 1990
Words:326
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