Since the late 1800s, scientists have been studying the northern sky looking for noctilucent clouds that shine in the dark. These are polar mesospheric clouds (PMC) and they are thin jets of ice crystals. To better study them, NASA has created artificial analogs of such clouds.
Noctilucent clouds form in late spring and summer over the North and South Poles.
It is best to observe such clouds at dusk, when the Sun illuminates them from over the horizon against the background of a dark sky. Not only is it a beautiful sight, mesospheric clouds give scientists clues about what is happening in the Earth’s atmosphere.
“The great interest in these clouds is due to their sensitivity. They emerge to the brink of survival 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 article in the Journal of Geophysical Research. “These clouds are a sensitive indicator of changes in the upper atmosphere. For example, changes in temperature and water vapor ”.
Collins and his collaborators suspected PMCs might be related to the 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 theory, scientists created their own PMCs. They were specially launched in January in the Arctic. This period is usually unfavorable for the appearance of such clouds – scientists wanted to avoid mixing artificially created and naturally occurring PMCs.
The Super Soaker rocket was launched in the early morning from the 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.
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.