Lenticular clouds (

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

: ''Lenticularis'' lentil-shaped, from ''lenticula''

lentil The lentil (''Lens culinaris'' or ''Lens esculenta'') is an edible legume. It is an annual plant known for its lens-shaped seeds. It is about tall, and the seeds grow in pods, usually with two seeds in each. As a food crop, the largest p ...

) are stationary

clouds In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid drop (liquid), droplets, ice crystals, frozen crystals, or other particulates, particles suspended in the atmosphere of a planetary body or similar space. ...

that form mostly in the

troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. Fro ...

, typically in parallel alignment to the wind direction. They are often comparable in appearance to a

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...

saucer A saucer is a type of small dishware. While in the Middle Ages a saucer was used for serving condiments and sauces, currently the term is used to denote a small plate or shallow bowl that supports a cup – usually one used to serve coffee ...

. Nacreous clouds that form in the lower stratosphere sometimes have lenticular shapes. There are three main types of lenticular clouds:

altocumulus Altocumulus (From Latin ''Altus'', "high", ''cumulus'', "heaped") is a middle-altitude cloud genus that belongs mainly to the ''stratocumuliform'' physical category characterized by globular masses or rolls in layers or patches, the individual ele ...

standing lenticular (ACSL),

stratocumulus A stratocumulus cloud, occasionally called a cumulostratus, belongs to a genus-type of clouds characterized by large dark, rounded masses, usually in groups, lines, or waves, the individual elements being larger than those in altocumulus, and th ...

standing lenticular (SCSL), and cirrocumulus standing lenticular (CCSL), varying in altitude above the ground. Because of their unique appearance, they have been suggested as an explanation for some unidentified flying object (

UFO An unidentified flying object (UFO), more recently renamed by US officials as a UAP (unidentified aerial phenomenon), is any perceived aerial phenomenon that cannot be immediately identified or explained. On investigation, most UFOs are ide ...

) sightings.

Formation and appearance

As air travels along the surface of the Earth, obstructions are often encountered, including natural features, such as mountains or hills, and artificial structures, such as buildings and other constructions, which disrupt the flow of air into "eddies", or areas of turbulence. When moist, stable air flows over a larger eddy, such as those caused by mountains, a series of large-scale standing waves form on the

leeward Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference ...

side of the mountain. If the temperature at the crest of the wave drops below the

dew point The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will ...

, moisture in the air may condense to form lenticular clouds. Under certain conditions, long strings of lenticular clouds may form near the crest of each successive wave, creating a formation known as a "

wave cloud A wave cloud is a cloud form created by atmospheric internal waves. Formation The atmospheric internal waves that form wave clouds are created as stable air flows over a raised land feature such as a mountain range, and can form either dir ...

". Those wave systems can produce large updrafts, occasionally enough for water vapour to condense and produce

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

. Lenticular clouds have been said to be mistaken for

UFOs An unidentified flying object (UFO), more recently renamed by US officials as a UAP (unidentified aerial phenomenon), is any perceived aerial phenomenon that cannot be immediately identified or explained. On investigation, most UFOs are ide ...

, because many of them have the shape of a "flying saucer", with a characteristic "lens" or smooth, saucer-like shape. Lenticular clouds generally do not form over low-lying or flat terrain, so many people may have never seen one before and don't know that they can exist. Bright colours (called

iridescence Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...

) are sometimes seen along the edge of lenticular clouds.

Flight

Pilots of powered aircraft tend to avoid flying near lenticular clouds because of the turbulence and sinking air of the rotor generated at the trailing edge of these clouds, but glider pilots actively seek them out in order to climb in the upward moving air at the leading edge. 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 cover great distances. , the gliding world records for both distance (over 3,000 km; 1,864 mi) and absolute altitude () were set using such lift.

Notes

References

External links

Standing Lenticular Clouds

Time Lapse of Lenticulars courtesy The Weather Nutz

BBC image gallery of lenticular clouds over Yorkshire in 2011Lenticular cloud seen from Palm Desert, California, in April 2008kcocco.com Altocumulus Lenticular Clouds, Wasatch Mountains, Utah
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San Francisco's Richmond District 2007: "Lennies" attacking the Richmond
{{DEFAULTSORT:Lenticular Cloud Cumulus Articles containing video clips

Formation and appearance

Flight

See also

Notes

References

External links