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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