Under certain conditions, private and commercial propeller planes and jet aircraft may induce odd-shaped holes or canals into clouds as they fly through them. These holes and canals have long fascinated the public and now new research shows they may affect precipitation in and around airports with frequent cloud cover in the wintertime.

Here is how: Planes may produce ice particles by freezing cloud droplets that cool as they flow around the tips of propellers, over wings or over jet aircraft, and thereby unintentionally seed clouds.

These seeding ice particles attract more moisture, becoming heavier, and then "snow out" or fall out of the cloud as snow along the path of a plane, thereby creating a hole in a cloud.

The effects of this inadvertent cloud seeding are similar to the effects of the intentional seeding of clouds: that is, both processes may increase the amount of precipitation falling from clouds.

The study, which was partially funded by the National Center for Atmospheric Research (NCAR) in Boulder, Colo., appears in the July 1, 2011 issue of the journal Science. NCAR is partially funded by the National Science Foundation.

"It is unlikely that the hole-punching ability of planes affects global climate," says Andrew Heymsfield of NCAR, the study's lead author.

But because the hole-punching ability of planes is particularly high when they fly through low subfreezing clouds, major airports that are covered in low clouds during winter are particularly vulnerable to precipitation associated with this inadvertent seeding.

This vulnerability means it may be necessary to de-ice planes more frequently, Heymsfield says. Also, because weather station records that climate modelers incorporate into climate predictions are housed at airports in the Arctic and Antarctic, climate predictions for these areas may be influenced by local weather conditions caused by inadvertent seeding near those airports.

Heymsfield says that his team's latest research built on a paper published by the team last year on a similar topic in the Bulletin of the American Meteorological Society by:

1) evaluating the exact types of aircraft that produce airplane induced holes and canals;
2) measuring the spread and persistence of the holes;
3) hypothesizing the mechanisms for the spread of holes;
4) numerically modeling the holes;
5) defining the processes for their spread and persistence; and
6) examining how often hole punched clouds and associate effects may occur near several major airports.

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