Method of predicting clear air turbulence could make flights smoother in the future

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Washington, October 2 : Researchers at the University of Georgia (UGA) have developed a new forecasting method to predict clear air turbulence (CAT) that could make flights smoother in the future.

This method would be able to help pilots chart new courses around patches of rough but clear air that can turn a flight dangerous.

"Our new method allows superior forecasts for CAT beyond the tools that have been in use," said John Knox, an assistant professor in the department of geography in UGA's Franklin College of Arts and Sciences.

"Commercial aircraft encounter severe-or-greater turbulence about 5,000 times each year, and the majority of these occur 10,000 feet above the Earth's surface. This new method gives pilots a way to avoid turbulence that's not associated with nearby thunderstorms or significant cloudiness," he added.

The new method predicts energy associated with gravity waves - phenomena in the atmosphere that look like ocean waves but which 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 Knox and his colleagues identified as a possible source of bumpiness comes from a different source. These waves are spontaneously generated 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 are usually invisible, and pilots often don't know they're present until they're flying right into them.

The new method is based on something called the Lighthill-Ford theory of spontaneous imbalance, developed by a British theoretician in the early 1990s.

Knox and his colleagues spent several years turning this theory into a forecast tool.

According to Knox, one problem with current CAT-forecasting models is that they are at least partly empirical.

"Current methods often rely on rules-of-thumb based on pilot experience that aren't always grounded in rigorous theory," he said.

The new method is based "on a single, consistent theory of spontaneous imbalance," and thus should at least theoretically be more reliable, he added.

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