On July 8, 2011 the Space Shuttle Atlantis launched for the very last time. On that historic day, as the world watched its last ascent up into orbit and commentators discussed the program's contributions to space flight and scientific research over 20 years, the shuttle helped spawn one last experiment. As the shuttle reached a height of about 70 miles over the east coast of the U.S., it released as it always did shortly after launch 350 tons of water vapor exhaust.
As the plume of vapor spread and floated on air currents high in Earth's atmosphere, it crossed through the observation paths of seven separate sets of instruments. A group of scientists, reporting in online in the Journal of Geophysical Research on August 27, 2012, tracked the plume to learn more about the airflow in the Mesosphere and Lower Thermosphere (MLT) -- a region that is typically quite hard to study. The team found the water vapor spread much faster than expected and that within 21 hours much of it collected near the arctic where it formed unusually bright high altitude clouds of a kind known as polar mesospheric clouds (PMCs). Such information will help improve global circulation models of air movement in the upper atmosphere, and also help with ongoing studies of PMCs.
"Polar mesospheric clouds are the highest clouds on Earth," says space scientist Michael Stevens at the Naval Research Laboratory, Washington, who is first author on the paper. "They shine brightly when the sun is just below the horizon and typically occur over polar regions in the summer. There is some evidence that they are increasing in number and people want to know if this is indicative of climate change or something else that we don't understand."
Since they shine at night, PMCs are also known as noctilucent clouds, and they can serve as an indicator not just of temperature changes, but also of how currents and waves move high in Earth's atmosphere. A visible cloud of water va
|Contact: Susan Hendrix|
NASA/Goddard Space Flight Center