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If the conditions are right, jet airplanes and turboprop aircraft can leave unusually shaped clouds in their wakes.
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Image Courtesy of Alan Sealls

Mysterious Clouds Produced by Aircraft

Without meaning to, airplanes can cause certain types of clouds to produce snow or rain. When the aircraft climb or descend through mid-level clouds, if the atmospheric conditions are right then the planes "seed" the clouds which cause the clouds to produce precipitation. Air is forced to expand over the wings as the aircraft moves forward, cools, and freezes the cloud droplets.

Another thing that happens as a result of this process is that the aircraft leave behind odd-shaped holes or channels in the clouds. These are called hole-punch or canal clouds. The key ingredient for developing these holes in the clouds is water droplets at subfreezing temperatures (below about 5 degrees Fahrenheit or -15 degrees Celsius). As air is cooled behind aircraft propellers or over jet wings, the water droplets freeze and drop toward Earth in the form of snow or rain.

Andrew Heymsfield, a scientist at the National Center for Atmospheric Research (NCAR) in Boulder, CO is the lead author of a paper that explains the research of this phenomenon. He explains, "Anytime aircraft fly through these specific conditions, they are altering the clouds in a way that can result in enhanced precipitation nearby."

In 2007 Heymsfield and his colleagues happened to fly through some falling snow west of Denver International Airport with an variety of instruments onboard their plane. They didn't notice anything unusual during the flight, but the data they collected showed a band of precipitation formed quickly in the area where they flew. The scientists went back to review their data and photos and noticed a hole in the altocumulus clouds they flew through, as well as a burst of snow that extended to the ground. Snow crystals began falling about five minutes after the aircraft flew through the cloud. The snowfall, in a band about 20 miles long and 2.5 miles wide, continued for about 45 minutes, resulting in about two inches of snow on the ground.

"This apparently happens frequently, embedded in the cloud layers," Heymsfield says. "You wouldn't necessarily see it from satellite or from the ground. I had no idea this was happening. I was sitting in back of the plane. And then this data set just fell in our laps. It was a lucky break."

Last modified August 10, 2010 by Becca Hatheway.

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