Magazine article USA TODAY

Searching for Cause of Clear Air Turbulence

Magazine article USA TODAY

Searching for Cause of Clear Air Turbulence

Article excerpt

It comes blasting out of the blue on your airplane flight: sudden bumpiness and sometimes even a violent plummeting. It arrives without warning, and it can be more than frightening since it causes tens of millions of dollars in injury claims every year. It is called clear air turbulence (CAT), and a new forecasting method could help pilots chart variable courses around these patches of rough but clear air that can turn an otherwise unremarkable flight into a nightmare, maintains McCann Aviation Weather Research, Inc., Overland Park, Kan.

Commercial aircraft encounter severe-or-greater turbulence about 5,000 times each year, and the majority of these episodes occur 10,000 feet above the Earth's surface. Pilots need a way to avoid turbulence that is not associated with nearby thunderstorms or significant cloudiness. The new method predicts energy associated with gravity waves--phenomena in the atmosphere that look like ocean waves but that can occur in clear air. They can be created by air flow over mountains, frontal boundaries, or other causes.

The type of gravity wave that the researchers identified as a possible source of bumpiness are generated spontaneously and associated with jet streams at high altitudes, near cruising levels for airplanes. When a plane flies through them, the sensation is like being in a small boat on a stormy sea but, where a boat's skipper can see rough sea, gravity waves in the air usually are invisible, and pilots often do not know they are present until they are flying right into them. …

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