July 1, 2011

Aircraft Affect Snowfall Around Airports

Researchers say that aircraft can lead to increased snowfall around the world's major airports.

New research shows that numerous private and commercial flights have been drilling holes and canals though clouds, influencing the snow and rainfall below them.

The inadvertent cloud-seeding effects are facilitated by the expansion and cooling of air behind a propeller aircraft's engine blades and over aircraft wings when supercooled cloud temperatures are about 14 degrees Fahrenheit and below. 

The drops in temperatures can be sufficient to spontaneously freeze the supercooled cloud droplets and form ice crystals, which then grow at the expense of the water droplets.

The researchers said the process then snowballs to produce a hole or a canal in the cloud layer that can continue expanding for hours, increasing precipitation in and below the cloud.

Researchers say this phenomenon may increase the need to de-ice planes more often in the future. 

Researchers from across the U.S. studied satellite images of these "hole-punch" or canal clouds in detail, and then used weather-forecasting computer models to simulate the clouds' growth and evolution.

The team said many different types of private and commercial propeller and jet aircraft can produce ice crystals and holes in supercooled clouds, which then spread and create snow in and below them.

These cloud covers have been documented for decades and are sometimes mistaken for rocket launches or U.F.Os.

"Whether an airplane creates a hole or a canal in the clouds depends on its trajectory," Andrew Heymsfield from the National Center for Atmospheric Research in Boulder, Colorado said in a statement. "When they climb through a supercooled cloud layer, they can just produce a hole. But when they fly level through the cloud layer, they can produce long canals."

According to the new research, these cloud layers can be found within 62 miles of the world's major airports as much as five to six percent of the time.

The researchers looked at archived aircraft flight information from the U.S. Federal Aviation Administration to find out what kind of aircraft had flown in a particular area on a specific day. 

They found that a different number of airplanes are able to produce these holes and canals.

"An aircraft propeller pushes air behind it, which generates thrust around the propeller tips," Heymsfield said in a statement. "This thrust, in turn, cools the air behind the propellers by up to 30 degrees Celsius (86 degrees Fahrenheit), freezing cloud droplets and leaving a stream of small ice particles trailing behind the propellers."

Heymsfield said the scientific investigation provided a thrill. "The most interesting part of this research to me is the physics"”and the fact that the production and spread of the holes and canals can now be explained," he said.

"Now, I'm off to the Virgin Islands to investigate more tropical cloud covers there."

The study was published in the July 1 issue of the journal Science.


Image 1: NASA's Terra satellite captured this image of hole-punch and canal clouds on Jan. 29, 2007. These unusual gaps in clouds are often caused by aircraft under certain atmospheric conditions. Credit: Jeff Schmaltz, MODIS Rapid Response Team, Goddard Space Flight Center

Image 2: Aircraft-induced hole observed at the West Antarctic Ice Sheet Divide Camp, Antarctica (79 28.058 °S 112 05.189 °W, 1806 m elevation) on Dec. 12, 2009, 1400 New Zealand Time. The cloud's bright cumuliform structure with gray fallstreaks below are visible. The hole first appeared on the horizon and then moved toward the camera. It is likely that a LC130 aircraft produced the ice that formed the hole. Photo provided by Eric Zrubek and Michael Carmody. For more information, please see Figure 1A in the manuscript. Credit: Image courtesy of Science/AAAS


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