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Topic: Noctilucent cloud

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	Noctilucent cloud - Wikipedia, the free encyclopedia
		Noctilucent clouds (also known as polar mesospheric clouds) are rare bright cloudlike atmospheric phenomena visible in a deep twilight (the name means roughly "night shining").
		Noctilucent clouds are not fully understood, as under most understood meteorological concepts, clouds generally are not able to reach such high altitudes, especially under such thin air pressures.
		Noctilucent clouds can be studied from the ground, from space, and in situ by sounding rockets; they are too high to be reached by weather balloons.
	en.wikipedia.org /wiki/Noctilucent_cloud (298 words)

	BBC - Weather Centre - Features - Understanding Weather - Nacreous and Noctilucent Clouds
		Noctilucent clouds look very similar to high cirrus but are bluish or silver in colour and are illuminated when the sun is below the horizon.
		These clouds are commonly known as 'mother of pearl clouds' due to the beautiful colours, and are at their most brilliant when the sun is some 5 to 10 degrees below the horizon.
		Noctilucent clouds are the highest clouds in the sky at a height of about 50 miles, which puts them at the top of the mesosphere.
	www.bbc.co.uk /weather/features/understanding/nacreous_noctilucent.shtml (595 words)

	Noctilucent cloud -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-11-06)
		Noctilucent clouds (also known as polar mesospheric clouds) are rare bright cloudlike atmospheric phenomena visible in a deep (The time of day immediately following sunset) twilight (the name means roughly "night shining").
		They are studied from the ground, from space, and in situ by (A research rocket used to obtain information about the atmosphere at various altitudes) sounding rockets; they are too high to be reached by (Large tough non-rigid bag filled with gas or heated air) balloons.
		The AIM (Man-made equipment that orbits around the earth or the moon) satellite mission, scheduled for launch in 2006, is dedicated to research into noctilucent clouds.
	www.absoluteastronomy.com /encyclopedia/n/no/noctilucent_cloud.htm (151 words)

	Theory of Noctilucent Clouds (Site not responding. Last check: 2007-11-06)
		Noctilucent clouds (NLC) are the highest clouds in the Earth's atmosphere, laying at the average height of about 83 km in the mesopause.
		The cloud particles are formed either by heterogeneous nucleation on small dust particles, or by a so-called ion-induced nucleation on certain ions in the polar mesopause.
		Thus, the polarization of noctilucent clouds is similar to the polarization of the background sky.
	www.meteo.helsinki.fi /~tpnousia/nlcgal/nlcinfo.html (1722 words)

	[No title]
		Noctilucent clouds are thin clouds which form at about the same height (about 82 km) and during about the same season as PMSE.
		Noctilucent clouds seen together with the PMSE in the lower panel above, are shown below.
		Noctilucent clouds seem to be increasing in occurrence (Gadsden, Journal of Atmospheric and Terrestrial Physics vol 52, p247, 1990) and some scientists believe this may be due to increased greenhouse gases in the atmosphere.
	spider.irf.se /program/afp/nlc (523 words)

	Colorado U. selected to build instruments, control cloud-monitoring satellite from campus
		Noctilucent, or "night-shining" clouds occur in the summer in the mesosphere, which is the coldest part of the atmosphere, said Thomas.
		Noctilucent cloud formation likely is hastened by increasing amounts of carbon dioxide in the atmosphere, he said.
		Thomas predicted in 1994 that the noctilucent clouds would continue to brighten and would be visible over the continental United States by the 21st century.
	www.eurekalert.org /pub_releases/2002-07/uoca-cus070302.php (633 words)

	CLOUD TYPES
		The funnel cloud is the visible portion of a tornado produced from clouds.
		A funnel cloud is not a tornado if the circulation is not in contact with the ground.
		These clouds are located 75 to 90 kilometers above the surface and are rarely seen due to their extremely low moisture density.
	www.theweatherprediction.com /clouds (705 words)

	Australian Antarctic Division - Noctilucent clouds
		One hypothesis is that the initial observation of noctilucent clouds was related to an increase in the number of observers of the twilight skies attracted by the spectacular displays resulting from the globally distributed volcanic debris of Krakatoa.
		Noctilucent cloud observations from north-west Europe over the last 30 years show an increasing trend in the number of nights on which the clouds are observed each summer season, superimposed on a decadal variability that appears to be solar-cycle related.
		Competing anthropogenic explanations for this increasing occurrence of noctilucent clouds focus on either excessive greenhouse cooling of the middle atmosphere or increased water vapour linked to increased methane release associated principally with intensive farming activities.
	www.aad.gov.au /?casid=2005 (447 words)

	Strange Clouds (Site not responding. Last check: 2007-11-06)
		Pettit estimated the height of the noctilucent clouds he saw at 80 to 100 km...
		"Noctilucent clouds are a relatively new phenomenon," says Gary Thomas, a professor at the University of Colorado who studies NLCs.
		Ordinary clouds, which are relatively close to Earth, get their dust from sources like desert wind storms.
	www.firstscience.com /SITE/ARTICLES/strange.asp (882 words)

	On the Diurnal Variation of Noctilucent Clouds
		The fact that noctilucent clouds are generally brighter and most widespread after midnight may account for the differences found between the earlier and more recent studies on the daily variation of noctilucent clouds frequency (Fogie and Haurwitz 1966; Schroeder 1968).
		Using the visual estimation of noctilucent cloud brightness, it should be noted that the clouds are usually very patchy, and observers often note the intensity of the bright patches in the display.
		The conclusions of Table 1 are the same as have been reported by earlier observers: (a) in general the noctilucent cloud displays show a variation of brightness; (b) most of the clouds have been noted after midnight with the intensity 3-5; (c) a maximum before local midnight is not found.
	verplant.org /history-geophysics/Diurnal_V/Main.htm (1348 words)

	Noctilucent Cloud
		Noctilucent cloud (NLC) is an atmospheric phenomena that is sometimes visible in the evening sky, at high latitudes, toward the sun, just after sunset, in the midsummer months.
		NLC are clouds, believed be ice crystals but because of their rarity and altitude very little is known about them.
		The dark wispy clouds just above the horizon are cirrus and cirrostratus at about FL360 and the noctilucent clouds are the white ones way above.
	www.chris.brady.ukgateway.net /noctilucent.htm (253 words)

	Carillon (Site not responding. Last check: 2007-11-06)
		Silvery-blue ice clouds known as noctilucent clouds that appear each year in the far northern and southern latitudes in the middle atmosphere were spotted over Colorado for the first time on June 22.
		Thomas, one of the world's leading experts on noctilucent clouds, predicted in 1994 that the clouds would brighten by five to ten times and be visible over the continental United States by the 21st century.
		Noctilucent cloud formation is likely hastened by increasing amounts of rising carbon dioxide from Earth.
	www.colorado.edu /Carillon/volume29/stories/1_ice_cloud.html (323 words)

	Noctilucent Clouds
		Noctilucent Cloud Season Upon Us Now that we have entered the beginning of June, members should be on the lookout for Noctilucent Clouds.
		They are fundamentally different from the usual tropospheric type clouds, which appear dark at night, and can in fact sometimes be seen silhouetted against the NLC making a lovely photograph.
		The upper limit of the clouds can sometimes also be of a lovely blue colour intermingled with streaks of silvery white.
	www.eaas.co.uk /news/noctilucent_clouds.html (812 words)

	Are 'Noctilucent Clouds' a thermometer for climate change?
		Scientists of the day figured the clouds were some curious manifestation of volcanic ash.Eventually the ash settled and the vivid sunsets of Krakatoa faded.
		How ice crystals form in the arid mesosphere is the essential mystery of noctilucent clouds.Ice crystals in clouds need two things to grow: water molecules and something for those molecules to stick to--dust, for example.
		Thomas notes that noctilucent clouds were first spotted during the Industrial Revolution--a time of rising greenhouse gas production.
	www.water-consciousness.com /must/must_article14.htm (912 words)

	AIM Mission To Study Noctilucent Clouds
		Noctilucent, or “night-shining,” clouds occur in the summer mesosphere, the coldest place in the atmosphere, said Thomas.
		Noctilucent cloud formation is believed to be hastened by increasing amounts of carbon dioxide in the atmosphere, Thomas said.
		Thomas predicted in 1994 that noctilucent clouds would continue to brighten and be visible over the continental United States by the 21st century.
	www.innovations-report.com /html/reports/earth_sciences/report-30434.html (632 words)

	Observing Noctilucent Clouds
		Most clouds exist within about 10 km of the Earth's surface; however, NLC exist at a height of 82 km.
		It is thought that noctilucent clouds exist at a temparature minumum in the Earth's atmosphere.
		If the noctilucent cloud height were to change, it would indicate a change in the temperature structure of the atmosphere.
	www.mikeoates.org /mas/observe/nlc (676 words)

	Clouds - 7 (Site not responding. Last check: 2007-11-06)
		This image shows a typical bands of cloud associated with a jet stream - the name given to narrow band of winds of at least 100 knots at 30,000 ft or higher.
		The cloud lines associated with the jet stream are in parallel bands, but perspective makes them appear to converge towards the horizon.
		These funnel clouds are like miniature tornados, whirling and twisting as they drift at the rear of the parent cloud.
	www.airbp.com /airbp/public/generalinterest/clouds/specialconditions.html (381 words)

	NLC FAQ (Site not responding. Last check: 2007-11-06)
		Noctilucent clouds (popularly referred to by the abbreviation "NLC") are high atmosphere cloud formations thought to be composed of small ice-coated particles; their precise nature remains a mystery.
		At times high cirrus cloud can appear to be brighter than the twilit background, especially when a bright moon is present or local light pollution problems are extreme.
		Binoculars can assist in correct identification; cirrus cloud tends to be nebulous when viewed through binoculars while NLC bears magnification, showing finer detail which the naked eye would otherwise be unable to resolve.
	www.nlcnet.co.uk /nlcfaq.htm (593 words)

	Mystery High Altitude Cloud, May 13, 1999
		The cloud pictured here (photos taken from Green Bay, Wisconsin looking northwest) was still sunlit long after cirrus clouds (5-6 km altitude) had gone dark.
		Although the last frames are quite dark, remnants of the cloud were visible and brighter than the sky even then.
		Noctilucent Cloud These super high-altitude clouds (50 km) are almost never seen below 50 degrees north so if this is a noctilucent cloud, it would easily be the southernmost ever seen.
	www.uwgb.edu /dutchs/geolwisc/weather/xcloud.htm (344 words)

	What are NLC? (Site not responding. Last check: 2007-11-06)
		Although the latter part of the nomenclature implicitly states that the phenomena are clouds they bare little resemblance to the common weather clouds with which we are all familiar.
		The clouds reside at an altitude of 80-85Km with an average altitude of 83Km.
		It is theorised that the clouds nucleate at the mesopause over several hours and during nucleation descend by a few Km to the altitude at which they are observed (Gadsden and Parviainen, 1995).
	freespace.virgin.net /eclipsing.binary/whatarenlc.html (1879 words)

	Noctilucent Clouds
		Noctilucent clouds are a mysterious upper atmospheric phenomenon that even scientists do not yet fully understand.
		These clouds are very high in the atmosphere, around 55 miles, and they will appear as very delicate pearly-white or bluish strands, not to be confused with cirrus clouds.
		During a fishing trip to Norse Lake in NW Ontario, Canada in June/2000, I was very lucky to get these photos of the noctilucent clouds, although they were somewhat obscurred by lower tropospheric clouds.
	www.nightskyevents.com /NoctilucentCloudsPage.html (288 words)

	NASA - I Love Those Blue Clouds
		"Noctilucent clouds have not only persisted, but also spread." A century ago the clouds were confined to latitudes above 50o; you had to go to places like Scandinavia, Russia and Britain to see them.
		Ice crystals in clouds need two things to grow: water molecules and something for those molecules to stick to -- dust, for example.
		Thomas notes that noctilucent clouds were first spotted during the Industrial Revolution -- a time of rising greenhouse gas production.
	www.nasa.gov /audience/forstudents/9-12/features/clouds_feature.html (901 words)

	Strange Clouds (Site not responding. Last check: 2007-11-06)
		The crew of the ISS have been observing strange "noctilucent" clouds hovering on the edge of space.
		The glowing clouds are too dim to see in broad daylight, but for a while after sunset, when the ground is dark and high clouds are still sunlit, noctilucent clouds can take your breath away.
		How tiny ice crystals form in the mesosphere is both the essential mystery of noctilucent clouds and, possibly, their link to something big: global warming.
	spacescience.com /headlines/y2003/images/4review_nlc.htm (1755 words)

	Geomagnetism and Aeronomy (Site not responding. Last check: 2007-11-06)
		Noctilucent and mesospheric clouds are formed close to the mesopause at a height of about 82 km, if temperature and humidity are favorable.
		The link between the occurrence of polar mesospheric clouds and noctilucent clouds and the mesospheric temperature profile points to the possibility of temperature measurements for predictions of polar mesospheric and noctilucent clouds occurrences.
		Comparison of seasonal variations of temperature and cloud occurrence has shown an agreement within 20%; thus this provides the possibility of prediction of polar mesospheric cloud and noctilucent cloud occurrences from temperature measurements.
	eos.wdcb.rssi.ru /transl/gma/9405/pap32.htm (205 words)

	noctilucent cloud -- Encyclopædia Britannica
		Located at an altitude of 85 kilometres, such a cloud is the highest on Earth and can be seen only when darkness has just set in on the planet.
		Clouds exert a significant effect on climate; they are generally associated with humid environments.
		During daylight and in summer, clouds keep temperatures from rising as high as they otherwise might by reducing the amount of heat received from the sun.
	www.britannica.com /eb/article-9056022?tocId=9056022 (795 words)

	MetLink/Noctilucent clouds/29 Jan (Site not responding. Last check: 2007-11-06)
		It was thus a noctilucent cloud situated at the top of the stratosphere at an altitude of about 85 km.
		However the other luminous cloud had disappeared, showing that it was much lower in the stratosphere, being a nacreous type of cloud.
		Thus the cloud could have been seen from anywhere in the British Isles, from the south coast appearing as a luminous band along the NW horizon.
	geography.radley.org.uk /metlink/news/noctiluc.html (350 words)

	NASA - Top Story - STUDY FINDS SPACE SHUTTLE EXHAUST CREATES NIGHT-SHINING CLOUDS - June 03, 2003
		Because of their high altitude, near the edge of space, noctilucent clouds shine at night when the Sun's rays hit them from below while the lower atmosphere is bathed in darkness.
		Noctilucent clouds, sometimes called polar mesospheric clouds when observed from space, are too thin to be seen by the naked eye in broad daylight.
		Stevens and colleagues find that the water contained in these clouds is consistent with the amount injected into the thermosphere by the shuttle on its ascent off the east coast of the United States.
	www.nasa.gov /centers/goddard/news/topstory/2003/0522shuttleshine.html (864 words)

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