Shuttle Launches Create
Arctic Clouds

Associated Press
Posted September 3, 2003

A benign and previously unknown aspect of shuttle flights links the space vehicles with the Arctic.

Researchers say the shuttle's exhaust, 97 percent of which is water vapor, quickly migrates to the highest reaches of the atmosphere above the Arctic.

There, the vapor spreads out about 50 miles high in Earth's mesosphere, just below the thermosphere, the air's highest layer, and settles to form a wispy type of cloud called noctilucent clouds.

The thin shroud of ice crystals is apparently too faint to be seen in daylight. But after the sun sets, and while it's not too far below the horizon, its rays illuminate the noctilucent clouds from below.

Noctilucent clouds typically form in summer, according to the May study, which was led by the Naval Research Laboratory and funded by the National Aeronautics and Space Administration and the Office of Naval Research.

The researchers concluded that summer launches of the shuttle created them.

The shuttle trails a giant plume of exhaust while rising through the atmosphere, Mike Stevens, the study's lead author, said earlier this summer on Arctic Science Journeys Radio at the University of Alaska Fairbanks.

"You can think of it as essentially a long garden hose that is on the order of (621 miles) long," Stevens said.

The scientists found that the amount of water in the clouds was nearly identical to the amount in the shuttle plume and they made the leap, Stevens said.

The shuttle's exhaust is not the only cause of such clouds, according to Doug Schneider, the writer and producer of Arctic Science Journeys Radio.

"They occur naturally," Schneider said. "But this plume provides for more ingredients."

Associated Press

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