Last Shuttle Flight Made Clouds Over Antarctica

High altitude clouds were detected over Antarctica shortly after the fateful launch of the space shuttle Columbia. The fact that some of these clouds are born out of shuttle exhaust may require a rethinking of their role as a diagnostic for global climate change.

Researchers using satellite and ground-based instruments tracked the exhaust plume from Columbia's liftoff from Kennedy Space Center in Florida on Jan. 16, 2003. The plume was roughly 650 miles long and two miles wide.

"Our analysis shows that the Columbia's exhaust plume approached the South Pole three days after launch," said Michael Stevens from the Naval Research Laboratory.

As with all shuttle launches, about 97 percent of this exhaust turns into water - a by-product of the liquid hydrogen and liquid oxygen fuel. The resulting 400 tons of extra water in the atmosphere has an observable effect on cloud formation.

Other rocket launches inject water into the atmosphere, but none so much as the shuttle launch vehicles. Because of low temperatures and the high concentrations of water from Columbia's exhaust, Stevens and his colleagues observed a significant increase in polar mesospheric clouds over Antarctica in the days following the launch.

Polar mesospheric clouds - also called noctilucent clouds - form in the summer over the poles at altitudes of about 52 miles (84 kilometers), making them the highest clouds in the Earth's atmosphere. They have been monitored in recent years because they are thought to be sensitive to the temperature and humidity of the atmosphere.

"Because the brightness, occurrence, and range of the clouds have been increasing, some scientists have suggested that they are indicators of global climate change," said Xinzhao Chu from the University of Illinois at Urbana-Champaign. "That role needs to be reconsidered, however, because of the potential influence of water vapor in shuttle plumes."

Shuttle missions have been on hold since 2003, after Columbia and its crew were lost during reentry. The return to flight is scheduled for July 13 of this year.

A paper describing these results appears in the July 6 issue of Geophysical Research Letters.

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