Lenticular cloud

 

Lenticular cloud
Dramatic "saucer cloud" over Campbell Mesa, Flagstaff, Arizona
Genus	Alto- (Latin for high) -cumulus (Latin: heap)
Species	lenticularis (Latin: lens-shaped)
Altitude	6,000-12,000 m (20,000-40,000 ft)
Classification	Family A (High-level)
Appearance	lens-like
Precipitation cloud?	Sometimes

Lenticular clouds (Altocumulus lenticularis) are stationary lens-shaped clouds that form at high altitudes, normally aligned perpendicular to the wind direction. Lenticular clouds can be separated into altocumulus standing lenticularis (ACSL), stratocumulus standing lenticular (SCSL), and cirrocumulus standing lenticular (CCSL). Due to their shape, they have been offered as an explanation for some Unidentified Flying Object (UFO) sightings.

Formation

Where stable moist air flows over a mountain or a range of mountains, a series of large-scale standing waves may form on the downwind side. If the temperature at the crest of the wave drops to the dew point, moisture in the air may condense to form lenticular clouds. As the moist air moves back down into the trough of the wave, the cloud may evaporate back into vapor. 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." The wave systems cause large vertical air movements and so enough water vapor may condense to produce precipitation. The clouds have been mistaken for UFOs (or "visual cover" for UFOs) because these clouds have a characteristic lens appearance and smooth saucer-like shape. Bright colors (called irisation) are sometimes seen along the edge of lenticular clouds. These 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.

Flight

Pilots 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 great distances. The current gliding world records for both distance (over 3,000 km; 1,864 mi) and altitude (15,460 m; 50,721 ft) were set using such lift.

Altocumulus lenticularis Gallery

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  Lenticular cloud above northern Presidential Range, New Hampshire, USA.

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  Lenticular Cloud Rings covering Mt. Jefferson, near Detroit Lake, Oregon, United States.

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  Stratocumulus lenticularis clouds near Homer, Alaska, United States.

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  Lenticular cloud above Skaftafell glacier in Iceland.

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  Lenticular Cloud over Santa Clarita, CA, United States.

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  Lenticular clouds form over Mt. Rainier, Washington, United States.

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  Altocumulus lenticularis often forms in the lee of mountains. Sierra Nevada, California, United States.

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  Lenticular clouds over Soda Lake, Mojave Desert, California, United States.

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  Lenticular Cloud over Squam Lake, New Hampshire, United States.

See also

• Cap Cloud

External links

• BBC image gallery of lenticular clouds over Yorkshire in 2011
• Lenticular cloud seen from Palm Desert, California, in April 2008
• kcocco.com Altocumulus Lenticular Clouds, Wasatch Mountains, Utah
• Picture of the Day 2009-01-21: A lenticular Cloud over New Zealand
• Sistek, Scott. "Mt. Rainier puts on a show!". KOMONews.com. http://www.komonews.com/weather/blog/35631614.html. Retrieved 2008-12-11. 
• APOD: Lenticular Clouds near Mt. Ranier, Washington, USA
• San Francisco's Richmond District 2007: "Lennies" attacking the Richmond