A NASA satellite has created a new map of so-called"night-shining clouds," which form at high altitudes on Earth andglow even after the sun sets.
These mysterious clouds, also called noctilucentclouds or Polar Mesospheric Clouds (PMCs), appear about 50 miles (80 km) aboveEarth's surface during the summer of each hemisphere ? from late May throughlate August in the north, and from late November to late February in the south.
NASA's Aeronomyof Ice in the Mesosphere (AIM) satellite has captured five complete polarseasons of noctilucent cloud coverage, showing that they can quickly form anddisperse, and that they are highly dependent on weather systems.
"The AIM findings have altered our previousunderstanding of why PMCs form and vary," said AIM principal investigatorJames Russell III of Hampton University in Virginia. "We have captured thebrightest clouds ever observed and they display large variations in size andstructure signifying a great sensitivity to the environment in which the cloudsform."
Noctilucent clouds are made of ice crystals that form whenwater vapor condenses onto dust particles at the extremely frigid temperaturesat high altitudes, between minus 210 to minus 235 degrees Fahrenheit (minus 134to -148 degrees Celsius).
They are visible even when the sky is dark because that highup, the clouds can continue to reflect sunlight after the sun has set below thehorizon. Their spectacular silvery-blue display can be seen well into thenight.
The AIM results show that the atmospheric temperature seemsto determine when the season for night-shiningclouds begins and how long it lasts.
"The cloud season abruptly turns on and off going fromno clouds to near complete coverage in a matter of days with the reversepattern occurring at the season end," Russell said.
AIM was launched in 2007 on a dedicated mission to studynoctilucent clouds and learn more about how and why they form, and why theyappear to be occurring at lower latitudes than ever before.
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