Why airplanes make it rain or snow
Aircraft create more rain near airports by punching holes in the clouds, effectively seeding the clouds, according to a new study of the phenomenon.
(Page 2 of 2)
This process is known as cloud seeding, and it can be done intentionally to alter weather. However, in this case, airplanes' cloud seeding effect is entirely accidental.Skip to next paragraph
Subscribe Today to the Monitor
To better understand hole-punch clouds, Heymsfield and colleagues followed the growth of 92 holes and canals — long streaks cut when a plane's path is more horizontal — through satellite data.Some reach lengths of more than 62 miles (100 kilometers) and lasted for four or more hours. Using Federal Aviation Administration tracking information, they found that a full spectrum of aircraft — from jets of all sizes to planes equipped with propellers — cut through the clouds.
They then compared satellite observations with simulations run using a weather model, and found that the airplane's introduction of ice created patterns of air movement upward in the hole and downward at the sides, causing the hole to expand for periods as long as an hour.
And finally, Heymsfield and colleagues looked at weather around seven airports, including major mid- latitude ones like Chicago O'Hare and one in Antarctica to see how frequently this accidental cloud seeding might happen.
Prop planes have as much as a 6 percent average probability of seeding clouds throughout a year, while jet aircraft are slightly less likely at 2 to 3 percent. This effect is stronger at higher latitudes because low-lying clouds are more common, he said.