London: Believe it or not, aero-planes influence local weather when they take off and land. A new study, published in the 'Science' journal, has found that aircrafts increase the chances of snow and rain during takeoff and landing, a finding based on satellite images of clouds around airports.

The phenomenon occurs when aircraft smash through clouds containing "super-cooled" water -- or water that exists as droplets of liquid at temperatures of minus 10C or below, say the researchers.

As an aero-plane passes quickly through a cloud, the air behind the wings and propellers expands and cools rapidly. These sudden drops in temperature can be enough to freeze droplets of super-cooled water, turning them into a stream of ice crystals.

Over time, ice crystals grow and affect neighbouring drops of water -- creating a hole in the cloud that expands for several hours and increasing the chances of snow or rain on the ground underneath.

Dr Andrew Heymsfield of the National Centre for Atmospheric Research in  Boulder, Colorado, said aircraft increased the chances of snow when they punched holes in clouds after taking off and when they created 'canals’ in clouds when descending.

"Whether an airplane creates a hole or a canal in the clouds depends on its trajectory. When they climb through a super-cooled cloud layer, they can just produce a hole. But when they fly through the cloud layer, they can produce long canals," he said.

The study found that super-cooled cloud layers are found with 62 miles of the world's major airports at least five per cent of the time. The cloud seeding effects are more noticeable closer to the north and south poles.

The researchers looked at 20 satellite images of cloud cover with holes suspended over Texas on one day in January 2007. Some of the holes were visible for more than four hours and grew more than 60 miles long.

The team then looked at flight data from the US Federal Aviation Administration to find out what aircraft had flown in each area, between 4.3 and five miles high, on that day.

They discovered that a range of aircraft can produce holes including jumbo jets, military planes and private single engine jets.

The researchers say it is unlikely that aircraft affect the global climate. However, it may increase the need to de-ice planes more often in the future, they say.

(Agencies)