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Aircraft Cause Additional Snowfall

A researcher at the the National Center for Atmospheric Research in Boulder, Colorado found that aircrafts that "punch holes" in clouds with water that has remained liquid below its freezing point (supercooled water), may cause increased snowfall. "The effect is similar to cloud seeding, which has been used in the past to influence the amount of precipitation falling from a cloud," a press release published by the American Association for the Advancement of Science (AAAS) stated. "But, new research shows that numerous private and commercial flights have been drilling holes and canals through clouds all along, influencing the snow and rainfall below them."

Andrew Heymsfield from the National Center for Atmospheric Research discovered that the expansion and cooling of air behind a propeller aircraft's engine blades and over aircraft wings can cause temperature drops that are significant enough to cause supercooled water to spontaneously freeze and form ice crystals. This may cause a chain reaction that can last for hours and produce snowfall that otherwise would not have occurred.

According to the research, supercooled 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 cloud-seeding effects caused by aircraft were more pronounced near the Earth's polar regions. Based on an analysis of satellite images of "punched" clouds, Heymsfield and his team found that some holes in the cloud were visible for more than four hours and grew to lengths greater than 62 miles long.

The researchers also identified a number of different airplanes that are able to produce such holes and canals, from large passenger jets and military planes to small turboprops and private, single-engine jets. "An aircraft propeller pushes air behind it, which generates thrust around the propeller tips," Heymsfield said. "This thrust, in turn, cools the air behind the propellers by up to 30 degrees Celsius, freezing cloud droplets and leaving a stream of small ice particles trailing behind the propellers."