Jet contrails may be beneficial to Kansas farmers

Topeka Capital-Journal, The, Aug 15, 2002 by Capital-Journal

Beginning on the afternoon of September 11, Kansans saw a sky that was unknown to all but the old-timers among us.

For three days, as the Federal Aviation Administration grounded all commercial and private aircraft, the sky was clear of jet contrails.

Without those wispy tails of cloud painted across the heavens by high-flying planes, the Kansas sky appeared as it last did in the 1940s or 1950s before the advent of high-volume jet travel.

Contrails are clouds created by the hot exhaust from jet engines. As the high altitude jet flies through ice-cold air, the engines burn jet fuel that creates a small amount of water vapor. This hot vapor shoots out the back of the engine, and within a second or two is chilled and frozen into ice crystals.

Only a small amount of the water comes from the jet fuel. Most of the contrail is created from the humidity that is already in the air that day. On days when the upper-level humidity is high, contrails are fat, long and persist for hours. For that reason, heavy contrails are a weather indicator. They imply very cold air aloft, packed with moisture --- an indicator of a potent weather system on the way.

For all its tragedy, Sept. 11 was a day of beautiful weather. Late summer high pressure had cleared the sky over most of the United States. You could have flown from coast to coast without encountering a single cloud. This isn't rare. Sky-clearing high pressure is a standard rite of late summer and early autumn. What made the sky so exceptionally clear was the lack of jet traffic.

Kansas has more jet contrails than just about any other state. We sit directly beneath the east-west flight corridor, and on any given day hundreds of commercial, private, and military jets are going over our heads. When a movie star in New York says he just flew in from Hollywood, or a movie star in Hollywood says she just flew in from New York, you can bet they flew right over your house. We should thank them.

The ice crystals in contrails are smaller than the crystals in normal cirrus clouds. That means contrails act as better reflectors. In the daytime they reflect some of the sun's energy back into space, meaning hot days won't be as hot. At night, the same contrails act as a blanket, reflecting the Earth's heat back down to the surface. Overnight lows aren't as chilly.

In other words, contrails have a positive effect on Midwest weather. They make the afternoon highs cooler and the overnight lows warmer. That is good for growing better and more crops.

This was proven on Sept. 11, 12 and 13, when U.S. air traffic came to a halt. With the exception of a few military flights (and Air Force One traveling from Louisiana to Nebraska and back to Washington) the skies over the Midwest were as clear as a bell. In areas like Kansas that normally experience a lot of contrails, the afternoon highs and the morning lows were almost four degrees farther apart. It means our days were two degrees hotter and our nights were two degrees cooler.

It seems, then, that contrails may be good for farming. Fewer blazing days and fewer morning freezes should help boost production by creating a more even temperature pattern, and a longer growing season.

Mel Gibson's latest movie, "Signs," required a few acres of trampled, ruined corn to create the necessary crop circles. This was a sad waste of food. But in zooming coast-to-coast to promote the film, Mel's jet travel may have benefited not just a few acres of corn, but hundreds of thousands. For this act of courageous, high- flying self-sacrifice, Mr. Gibson is to be commended for his hard work to help America's farmers.

Bruce Jones is chief meteorologist

for KSNT-TV 27.