In their twilight manifestation, they are observable from the ground at latitudes between 50° and 65°. They are also called Polar Mesospheric Clouds (PMCs), night-shining clouds and look out for #NCL or #NCLnow for the next view . Polar mesospheric clouds form between 76 to 85 kilometers (47 to 53 miles) above Earth’s surface when there is sufficient water vapor at these high altitudes to freeze into ice crystals. They form in the polar summer mesopause, the coldest region in the atmosphere. Measurements from space of the Earth's ultraviolet albedo are affected by scattering of sunlight from polar mesospheric clouds (PMC). Solar backscatter ultraviolet (SBUV) PMC observations in July 1999 indicate a burst of activity persisting for ∼8 days after a space shuttle launch and averaging 262 ± 52 t near 4.7 local time. Polar Mesospheric Clouds (PMC) are the space manifestation of noctilucent clouds, visible during high-latitude summertime twilight. PMC were first sighted by astronauts in the mid-1960's, but their full transpolar extent was not appreciated until the Ogo-6 airglow experiment in 1969. Night clouds or noctilucent clouds are tenuous cloud-like phenomena that are the "ragged-edge" of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. Polar mesospheric clouds are thin layers of nanometer-sized ice particles that occur at altitudes between 82 and 87 kilometers in the high-latitude summer mesosphere. The name means roughly night shining in Latin..
A fascinating product of the extremely cold summertime polar mesopause (at 85 km) is the existence of ice clouds, called Polar Mesospheric Clouds (PMC). NASA.gov brings you the latest images, videos and news from America's space agency.
They are also called Polar Mesospheric Clouds (PMCs), when looking from space. Solar backscatter ultraviolet (SBUV) PMC observations in July 1999 indicate a burst of activity persisting for ∼8 days after a space shuttle launch and averaging 262 ± 52 t near 4.7 local time. Polar mesospheric clouds generally increase in brightness and occurrence frequency with increasing latitude, from about 60 degrees to the highest latitudes observed (85 degrees). So far, no apparent dependence on longitude has been found, nor is there any evidence of a … [1] We infer the polar mesospheric cloud (PMC) mass throughout the Arctic summer using results from two sets of satellite observations and a microphysical model. We have examined 8 years of solar backscattered ultraviolet (SBUV) albedo data and find evidence of an annual occurrence of PMC in the summertime polar cap regions of both hemispheres. Noctilucent clouds, also known as polar mesospheric clouds, are very high (typically 80 km or 50 mi) cloud-like phenomena in the upper atmosphere, visible in a deep twilight.They are made of crystals of water ice.
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