Jet contrails can affect temperatures on the ground
Digital Reporter
Friday, June 19, 2015, 2:14 PM - Look up outside on a daily basis, and you're likely to see white contrails crossing the sky. But what has long been an ordinary sight has proven to have extraordinary powers when it comes to the weather.
The clouds of ice water crystals, though hanging at extremely high elevations, can effect on surface temperature and local, according to a team of geographers from Pennsylvania State University.
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For contrails to form, the atmosphere at the level the jet is flying must be cold enough that the moisture from the jet exhaust freezes into ice crystals.
There also must be enough moisture in the air that the clouds that form remain in the sky for at least a few hours as persisting contrails.
"Research done regarding September 2001, during the three days following 9-11 when no commercial jets were in the sky, suggested that contrails had an effect," said Andrew M. Carleton, professor of geography in a statement. "But that was only three days. We needed to look longer, while jets were in the air, to determine the real impact of contrails on temperature and in terms of climate."
Researchers analyzed daily temperatures taken at two weather stations identified as "contrail" sites -- one in the southern U.S. in January and another in the Midwest in April.
They then compared the data with two "non-contrail" sites that were similar in land cover and soil composition.
It was discovered the contrails are capable of decreasing maximum temperatures and increasing minimum temperatures. In the south, this caused a Fahrenheit reduction of about 6 degrees. In the Midwest, the reduction was about 5 degrees.
It's hoped the findings will allow for better weather forecasting.
"Weather forecasting of daytime highs and lows do not include contrails," Carleton said in a statement.
"If they were included in areas of contrail outbreaks, they would improve the temperature forecasts."
Source: Penn State
