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American Association for the Advancement of Science

Planes punch holes in the clouds, making it snow

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 12 Dec 2009, 1400 New Zealand Time. The cloud's bright cumuliform structure with grey 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.
[Image courtesy of Science/AAAS]

Many clouds in the sky contain water that is "supercooled," or able to stay in liquid form at temperatures below zero degrees Celsius. In fact, supercooled water can remain as a liquid all the way down to -40 degrees Celsius. However, when planes fly through clouds that hold supercooled water, they often punch holes right through them. And researchers now say that this phenomenon can lead to increased rain and snowfall on the ground below.

This effect, which is reported by Andrew Heymsfield and colleagues in the 1 July issue of the journal Science, is similar to cloud-seeding operations, which have been used to increase the amount of rain coming from a cloud in the past. But, this new research shows that many private and commercial flights have been "seeding" clouds all along—punching holes in them and altering the snow and rainfall below on a regular basis.

The researchers studied satellite images of these types of clouds with holes in them, and then used weather-forecasting computer models to predict the clouds' growth and evolution. Heymsfield and his colleagues concluded that many different types of propeller and jet aircraft produce ice crystals and holes in supercooled clouds which then spread and create snow below them.

According to the researchers, this accidental type of cloud seeding will probably not affect the global climate. But, since many major airports have low cloud cover in the wintertime, it may increase the need to de-ice planes more often in the future. Apparently, these supercooled cloud layers can be found within 62 miles (100 kilometers) of the world's major airports as much as five to six percent of the time.