| 词条 | Lenticular cloud |
| 释义 |
|name=Lenticular cloud |image location=Lenticular Cloud over Harold's Cross Dublin Ireland 30-6-15.jpg |image name=Dramatic lenticular cloud formation over Harold's Cross, Dublin |abbreviation= |genus=Stratocumulus, altocumulus, cirrocumulus |species=lenticularis (Latin: lens-shaped) |variety= |altitude_m=up to 12,000 |altitude_ft=40,000 |level=low, middle, high |appearance=lens-like, Saucer-shaped }} Lenticular clouds (Altocumulus lenticularis in Latin) are stationary clouds that form mostly in the troposphere, typically in perpendicular alignment to the wind direction. They are often comparable in appearance to a lens or saucer. Nacreous clouds that form in the lower stratosphere sometimes have lenticular shapes. There are three main types of lenticular clouds: altocumulus standing lenticular (ACSL), stratocumulus standing lenticular (SCSL), and cirrocumulus standing lenticular (CCSL), varying in altitude above the ground. Because of their unique appearance, they have been brought forward as an explanation for some unidentified flying object (UFO) sightings. Formation and appearanceAs air travels along the surface of the Earth, obstructions are often encountered. These include both natural features of the Earth, such as mountains or hills, and man-made structures, such as buildings and other structures. These disrupt the flow of air into "eddies", or areas of turbulence influenced by these obstructions. When moist, stable air flows over a larger eddie, like those caused by mountains, a series of large-scale standing waves form on the leeward side of the mountain. If the temperature at the crest of the wave drops below the local dew point, moisture in the air may condense to form lenticular clouds. Under certain conditions, long strings of lenticular clouds can form near the crest of each successive wave, creating a formation known as a "wave cloud." These wave systems can produce large updrafts, occasionally enough for water vapour to condense and produce precipitation.[1] Lenticular clouds have been mistaken for UFOs (or "visual cover" for UFOs), particularly in the shape of a "flying saucer", because these clouds have a characteristic lens appearance and smooth saucer-like shape; also, because lenticular clouds generally do not form over low-lying or flat terrain, many people may have never seen one before and don't know that they can exist.[2]{{refn|group=nb|Lenticular clouds have also been known to form in cases where a mountain does not exist, but rather as the result of shear winds created by a front.}} Bright colours (called iridescence) are sometimes seen along the edge of lenticular clouds.[3] FlightPilots of powered aircraft tend to avoid flying near lenticular clouds because of the turbulence of the rotor systems that accompany them, but glider pilots actively seek them out. The precise location of the rising air mass is fairly easy to predict from the orientation of the clouds. "Wave lift" of this kind is often very smooth and strong, and enables gliders to soar to remarkable altitudes and to great distances. {{As of | 2016}} the gliding world records for both distance (over 3,000 km; 1,864 mi){{citation needed|date=February 2016}} and absolute altitude (15,460 m; 50,721 ft)[4] were set using such lift. See also
Notes1. ^{{cite web|title=Altocumulus Standing Lenticular Clouds|url=https://www.weather.gov/abq/features_acsl|website=National Weather Service|publisher=NOAA|accessdate=9 March 2018}} 2. ^{{cite web|title=Lenticular clouds look like UFOs|url=http://earthsky.org/earth/best-photos-beautiful-lenticular-clouds-around-the-world|website=EarthSky}} 3. ^Atmospheric Optics: Iridescent Clouds 4. ^{{cite web | url = http://www.fai.org/record-gliding/ | title = Gliding World Records | access-date = 2016-02-01}} References{{reflist}}External links
|url=http://www.komonews.com/weather/blog/35631614.html |accessdate=2008-12-11 |title=Mt. Rainier puts on a show! |first=Scott |last=Sistek |publisher=KOMONews.com}}
2 : Cumulus|Articles containing video clips |
| 随便看 |
|
开放百科全书收录14589846条英语、德语、日语等多语种百科知识，基本涵盖了大多数领域的百科知识，是一部内容自由、开放的电子版国际百科全书。