Nacreous Clouds

nacreous clouds

[′nā·krē·əs ′klau̇dz]
(meteorology)
Clouds of unknown composition, whose form resembles that of cirrus or altocumulus lenticularis, and which show very strong irisation similar to that of mother-of-pearl, especially when the sun is several degrees below the horizon; they occur at heights of about 12 or 18 miles (20 or 30 kilometers). Also known as mother-of-pearl clouds.

Nacreous Clouds

 

thin, translucent clouds that occur at high elevations (about 22–30 km). They are observed rather infrequently, usually at latitudes of 55°-60° just before sunrise or just after sunset (against the daytime background of diffused light they are invisible).

References in periodicals archive ?
Also known as nacreous clouds, they form at altitudes of 20-30 kilometers at very low temperatures (about -95[degrees]F), and because of their slimness are generally only visible before sunrise or after sunset.
The iridescent nacreous clouds - considered rare as they are usually found only in very cool air - come from ice crystals refracting the sun's rays.
Incredibly, gusts reached 144mph in the Cairngorm mountains and there were nacreous clouds, which the Met Office said are usually seen in polar regions.
Meteorological officer Renae Baker captured spectacular images of the nacreous clouds, on July 25.
Meteorological officer Renae Baker captured spectacular images of the nacreous clouds, also known as polar stratospheric clouds, on July 25.
A few of her paintings have only clouds, but many feature colorful and unusual atmospheric sightings such as nacreous clouds, eclipses or rosy lightning.