Polar mesospheric clouds

{
  "id": "MLC-T-MET-008027",
  "term": "Polar mesospheric clouds",
  "field": "Meteorology and atmospheric science",
  "definition": "Extremely high-altitude clouds, also known as noctilucent clouds, that form in the mesosphere at altitudes of about 76 to 85 kilometers during summer in the polar regions. They are composed of tiny ice crystals that become visible when illuminated by sunlight from below the horizon while the ground is in darkness. Their formation is sensitive to very low temperatures and water vapor concentrations in the upper atmosphere.",
  "abbreviation": "PMC",
  "url": "https://mlchart.com/terminology/meteorology/polar-mesospheric-clouds/"
}