Air traffic may intensify precipitation

A new study indicates that planes that are taking off and landing may increase rainfall in the vicinity of airports, an observation that helps nowcast weather conditions at these locations.

Have you noticed that snow and rainfall are sometimes more intense close to airports? This phenomenon also attracted the attention of Dmitri Moisseev, an associate professor working at the Institute for Atmospheric and Earth System Research INAR, University of Helsinki.

He took a look at the precipitation data collected by weather monitoring equipment at Kumpula Campus. Snow and rainfall seemed to intensify closer to Helsinki Airport, in certain weather conditions.

Moisseev and his research group began looking into the origins of this phenomenon, revealing aircraft arriving at or departing from the airport as the culprit.

When aircraft with their large wings whoosh through clouds, which are composed of extremely cold (below freezing) water droplets, the clouds’ temperature momentarily drops even further, freezing the droplets that have so far remained liquid despite the freezing temperatures. The resulting crystals fall through the rain clouds below, intensifying precipitation as much as tenfold.

Falling ice crystals alone are unable to cause rain or snowfall; rather, they can only intensify pre-existing precipitation.

“What is interesting is that the phenomenon is not caused by aircraft emissions, but the aircraft themselves. Even entirely emission-free planes, if such were in existence, would still intensify precipitation near airfields,” Moisseev explains.

The group investigated the cause of intensified precipitation by analysing weather observations made close to the airport during a period of 11 years, comparing them with aircraft flight paths.

Meteorologists can utilise the observation made by Moisseev’s group when forecasting weather conditions at airports. Predicting snow and rainfall is important for the smooth flow of air traffic.

Inadvertent localized intensification of precipitation by aircraft, the research article authored by Moisseev's group, was published in the journal of the American Geophysical Union.

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Atmospheric and Earth System Research INAR