Noctilucent clouds form in late spring and summer over the North and South Poles.
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“Great interest in these clouds is due to theirsensitivity. They arise at the edge of viability in the upper atmosphere, where it is incredibly dry and cold, explains Richard Collins, a space physicist at the University of Alaska and lead author of a new paper in the Journal of Geophysical Research. — Such clouds are a sensitive indicator of changes in the upper atmosphere. For example, changes in temperature and water vapor."
Polar mesospheric clouds captured by the crew of Expedition 31 to the International Space Station on June 13, 2012. Photo: NASA Johnson Space Center / International Space Station
Collins and his staff suspected that PMCcan be associated with cooling in the upper atmosphere, and wanted to understand the microphysics of this process. In a new article, scientists shared the results of NASA's Super Soaker mission, a small suborbital rocket launched in Alaska. Thanks to the mission, scientists have found that water vapor in the Earth's upper atmosphere dramatically lowers the ambient temperature and causes bright, glowing clouds.
To test the mesospheric cloud theory,scientists created their own artificial PMCs in January in the Arctic. The timing was not chosen by chance. The winter period is unfavorable for the appearance of such clouds in the natural environment - scientists wanted to avoid mixing artificially created and naturally occurring ones.
The Super Soaker rocket was launched in the early morning withthe Poker Flat research site in Fairbanks, Alaska. Upon reaching an altitude of 85 km, the team provoked an explosion of a canister with 206 liters of water. Eighteen seconds later, the ground-based laser radar beam detected a faint PMC echo.
Ground test of water canister release. Credit: NASA Flight Complex Wallops.
The researchers incorporated these measurements into a model that simulates PMC production. They wanted to understand how the air into which the water was released had to change in order to create the necessary clouds.
The NASA mission is the first time anyone has experimentally demonstrated that cloud formation in the mesosphere is directly related to cooling by water vapor itself.
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