Mysterious Gravity Waves May Explain Clear-Skies Turbulence

Gravity waves may explain mysterious airplane turbulence despite clear skies. CREDIT: Kuster & Wildhaber Photography, via Flickr View full size image

SAN FRANCISCO — Gravity waves, mysterious waves that ripple unseen throughout the atmosphere, may be a major source of airplane turbulence, a new study suggests.

The new findings, presented Tuesday (Dec. 4) here at the annual meeting of the American Geophysical Union, may help explain why planes get shaky in apparently clear skies. Forecasting those waves may allow planes to reroute around them.

"Just like waves on the ocean, as they approach a beach, they can amplify and break. Gravity waves in the atmosphere can amplify and break, and we're finding now that's a major contributor to turbulence in the atmosphere that affects aircrafts."

Gravity waves form when air traveling up and down in the atmosphere meets resistance. For instance, clouds rising in the troposphere, the lower level of the atmosphere where air mixes freely, will bump up against the boundary of the much more stable stratosphere, forming ripples in the process. These waves can travel up to 180 miles (300 kilometers) before breaking, said Robert Sharman, a meteorologist at the National Center for Atmospheric Research (NCAR), who conducted the study.

"They're waves running around in the atmosphere all the time," Sharman told LiveScience.

Sharman and his colleagues wanted to understand when and where these waves occur. They collected data from commercial aircraft flight recorders, which record the location, duration and intensity of turbulence.

Then they recreated these turbulent events using a computer simulation that models the atmosphere. They found that gravity waves "break" on the surfaces of planes, just like ocean waves breaking on the beach, causing much of the turbulence that occurs out of the blue in clear air. In the past, pilots thought airplanes moving up and down in the jet stream caused such turbulence.

Many of the waves were formed in storm clouds that tracked the jet stream, but traveled miles away and broke in areas where airplanes were flying. Big mountains like the Colorado Rockies often form gravity waves as air flows over the mountains and then overshoots as it reaches the other side. [Photos: The World's Tallest Mountains]

Luckily, gravity waves don't span a large height in the atmosphere, so it's pretty easy for airplanes to avoid such waves, Sharman said.

"They could either climb over it or go beneath it," he said.

The team is now using their simulations to forecast gravity waves throughout the world. While the forecasts can predict the waves' occurrence most of the time, they would need to reach about 85 percent accuracy before pilots would use such predictions to avoid choppy air, he said.

"Anytime they change course, it costs the airlines fuel. They have to be pretty certain that that forecast is right before they'll make any deviation," he said.

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