March 11, 2009

Study finds causes of Atlanta tornado

U.S. scientists say the only tornado to hit downtown Atlanta in recorded history may have formed because of previous rainfall in the drought-stricken area.

On March 14, 2008, a tornado swept through downtown Atlanta, with 130 mile-per-hour winds. National Aeronautics and Space Administration officials said the event was so rare in an urban landscape that NASA funded a study to determine what weather and climatological conditions might have combined to cause such a storm.

The Atlanta tornado, though forecasted well, caught us by surprise because it evolved rapidly under very peculiar conditions during a drought and over a downtown area, said Purdue University Assistant Professor Dev Niyogi, lead author of the study.

Researchers from Purdue and the University of Georgia determined the scattered rainfall created pockets of high humidity between areas of warm, dry air. The wet and dry areas may have acted as weak atmospheric fronts or may have promoted air circulation and evaporation that could have intensified the storms.

NASA said the scientists also found evidence the heat-retaining effects of Atlanta's urban structures caused moisture to rise quickly, creating a thunderstorm pump that can fuel or intensify storms.

The researchers detailed their findings earlier this year during the annual meeting of the American Meteorological Society.