Noctilucent Cloud

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noctilucent cloud

[¦näk·tə¦lü·sənt ′klau̇d]
A cloud of unknown composition which occurs at great heights and high altitudes; photometric measurements have located such clouds between 45 and 54 miles (75 and 90 kilometers); they resemble thin cirrus, but usually with a bluish or silverish color, although sometimes orange to red, standing out against a dark night sky.

Noctilucent Cloud


a type of luminous, transparent cloud that sometimes appears in the upper part of the mesosphere at altitudes of 70–90 km. The structure of noctilucent clouds is somewhat similar to that of light cirrus clouds. Noctilucent clouds consist of aggregations of particles 10-4–10-5 cm in size that scatter sunlight. Such particles may consist of ice crystals formed upon condensation of water vapor that has been borne upward to high altitudes, or they may be volcanic or cosmic (meteoric) dust. It is possible that ice crystals form only around dust particles.

Noctilucent clouds were first investigated by V. K. Tseraskii in 1885. They are observed in the northern hemisphere between the latitudes of 45° and 70° and in the southern hemisphere between the latitudes of 40° and 65°. They occur only during the warm part of the year—from May through August in the northern hemisphere, with a maximum number of occurrences in July. The annual number of recorded occurrences observed from a given point may be as high as 20 to 30. Noctilucent clouds exist for periods of several minutes to several hours. In appearance they assume four basic configurations: gauze, bands, combs, and whirls. For observations from the ground, the best visibility is during nautical twilight, when the sun is 6°-12° below the horizon. Noctilucent clouds can also be observed during daylight if the observation equipment is raised aloft to high altitudes. Observations of noctilucent clouds are used to obtain data on the winds prevailing at the altitude of formation.


Bronshten, V. A., and N. I. Grishin. Serebristye oblaka. Moscow, 1970.


References in periodicals archive ?
Also known as Polar mesospheric clouds, these are extremely high altitude clouds of ice crystals in the upper atmosphere.
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.
The satellite observed a second northern season of Polar Mesospheric Clouds (PMCs), which are the Earth's highest clouds.
The AIM satellite mission will explore Polar Mesospheric Clouds (PMCs), also called noctilucent clouds.
The scientists also used their lasers to study polar mesospheric clouds.
Gardner's team found that the mesospheric clouds over the South Pole were, on average, at an altitude of 85.
SHIMMER's objectives were to make measurements of hydroxyl (OH) in the middle atmosphere and observe Polar Mesospheric Clouds, Earth's highest altitude clouds (82 km).
The extended mission allowed SHIMMER to collect an additional 18 months of observations of Polar Mesospheric Clouds which are being used to validate the Space Science Division's new high-altitude extension of the Navy's Operational Global Atmospheric Prediction System (NOGAPS).
He has worked on spacecraft rendezvous theory, terrestrial polar mesospheric clouds, galactic astrophysics and studies of tenuous satellite atmospheres, including the atmosphere of the moon.
Mesospheric clouds create an icy membrane about 50 miles above the surface at the edge of space.
Orbital Designed, Manufactured and Tested AIM Satellite for NASA to Study Polar Mesospheric Clouds
The scientific mission of the AIM satellite program is focused on the study of Polar Mesospheric Clouds (PMCs) that form about 50 miles above the Earth's surface in the summer months, primarily in the polar regions.