Study: Airplanes cause rain near airports

WASHINGTON -- The planes make rain that wets airport terrain.

Airplanes flying through supercooled clouds near airports can cause condensation resulting in more snow and rain nearby, according to a new study.

The correct conditions for this inadvertent weather modification occur about 5 percent of the time -- but 10 to 15 percent in winter -- according to Andrew J. Heymsfield of the National Center for Atmospheric Research in Boulder, Colo., lead author of the study in today's edition of the journal Science.

Aircraft take off into the wind, he noted, so if they are generating extra ice particles upwind of an airport, the result can be snow right on the airport. That might mean planes will require more de-icing, he said, though other researchers weren't sure.

The team was investigating holes or canals that are sometimes seen drilled in clouds after an airplane has passed through.

Studying six commercial airports, they found that increased snow and rainfall occurs in areas where the unusual cloud holes appear, usually within 60 miles of the airport. The added rain or snowfall occurred when conditions in the clouds were supercooled. That means the clouds were made up of water droplets that were colder than freezing, but had not yet frozen.

When an airplane passes through one of these clouds, the movement of air around the tips of the propeller, or over the wings of a jet, causes a sudden cooling of the air, sometimes down to the critical point where the droplets freeze. They then can fall to earth as snow or rain.

-- AP