Areas near airports can experience an increase in rain and snow when aircraft take off and land under certain atmospheric conditions, U.S. researchers say.
Scientists at the National Center for Atmospheric Research say the small but measurable increase is the result of a phenomenon called hole punch when planes fly through certain mid-level clouds, forcing nearby air to rapidly expand and cool.
This causes water droplets in the atmosphere to freeze to ice and then turn to snow as they fall toward the ground, leaving behind gaps in the clouds, an NCAR release said Thursday.
The researchers used satellite images and weather computer models to examine this type of inadvertent cloud seeding near six commercial airports: London Heathrow, Frankfurt, Charles De Gaulle (Paris), Seattle-Tacoma, O'Hare (Chicago), and Yellowknife (Northwest Territories, Canada), as well as Byrd Station in Antarctica.
Depending on the airport and type of plane, they found, the right atmospheric conditions typically exist up to 6 percent of the time.
"It appears to be a rather widespread effect for aircraft to inadvertently cause some measurable amount of rain or snow as they fly through certain clouds," NCAR scientist Andrew Heymsfield said. "This is not necessarily enough precipitation to affect global climate, but it is noticeable around major airports in the midlatitudes."