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noctilucent clouds
noctilucent clouds (NLC) Literally, ‘night-shining’ blue–silver clouds seen in late or early twilight during the summer from high temperate latitudes. Noctilucent clouds result from water vapour condensing on nuclei (possibly meteoric or volcanic debris) at altitudes of around 82–85 km, close to the mesopause. The clouds are extremely tenuous, and are seen only when the Sun lies between 6° and 16° below the horizon, appearing bright by contrast with the twilight sky. Noctilucent clouds lie five times higher than the loftiest clouds in the troposphere, and are distinct from cirrus clouds to which they bear a superficial resemblance. In particular, noctilucent clouds may be identified by their delicate, feathery, interwoven herring-bone structure. They are more common in years of low solar activity, and there is evidence that they are becoming more frequent.
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"noctilucent clouds." A Dictionary of Astronomy. 1997. Encyclopedia.com. 30 May. 2012 <http://www.encyclopedia.com>. "noctilucent clouds." A Dictionary of Astronomy. 1997. Encyclopedia.com. (May 30, 2012). http://www.encyclopedia.com/doc/1O80-noctilucentclouds.html "noctilucent clouds." A Dictionary of Astronomy. 1997. Retrieved May 30, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-noctilucentclouds.html |
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noctilucent clouds
noctilucent clouds (luminous night clouds) Type of clouds, occurring at 80–85 km altitude, near the upper limit of the stratosphere, characterized by a blue to yellow hue, and similar in appearance to cirrostratus. The clouds are seen on summer nights at latitudes between about 50° and 65° in both northern and southern hemispheres; they move rapidly, at speeds up to 300 knots, often in a wave formation.
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AILSA ALLABY and MICHAEL ALLABY. "noctilucent clouds." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 30 May. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "noctilucent clouds." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 30, 2012). http://www.encyclopedia.com/doc/1O13-noctilucentclouds.html AILSA ALLABY and MICHAEL ALLABY. "noctilucent clouds." A Dictionary of Earth Sciences. 1999. Retrieved May 30, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-noctilucentclouds.html |
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noctilucent clouds
noctilucent clouds(luminous night clouds) Clouds, occurring at 80–85 km altitude, near the upper limit of the stratosphere, which are blue to yellow in colour and similar in appearance to cirrostratus. The clouds are seen on summer nights at latitudes between about 50° and 65° in both hemispheres; they move rapidly, at speeds up to 300 knots (556 km/h), often in a wave formation.
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Cite this article
MICHAEL ALLABY. "noctilucent clouds." A Dictionary of Ecology. 2004. Encyclopedia.com. 30 May. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "noctilucent clouds." A Dictionary of Ecology. 2004. Encyclopedia.com. (May 30, 2012). http://www.encyclopedia.com/doc/1O14-noctilucentclouds.html MICHAEL ALLABY. "noctilucent clouds." A Dictionary of Ecology. 2004. Retrieved May 30, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O14-noctilucentclouds.html |
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