Lenticular cloud

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Lenticular cloud
Dramatic Lenticular Cloud Formation over Harold's Cross, Dublin
Dramatic Lenticular Cloud Formation over Harold's Cross, Dublin
Genus Stratocumulus, altocumulus, cirrocumulus
Species lenticularis (Latin: lens-shaped)
Altitude up to 12,000 m
(up to 40,000 ft)
Appearance lens-like, Saucer-shaped
Precipitation cloud? Sometimes

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

Formation

As air flows along the surface of the Earth, it encounters obstructions. These are man-made objects, such as buildings and bridges, and natural features, like hills, valleys, and mountains. All of them disrupt the flow of air into eddies. The strength of the eddies depends on the size of the object and the speed of the wind. It results in turbulence classified as ‘mechanical’ because it is formed through the “mechanical disruption of the ambient wind flow”. 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 movement, enough that water vapor may condense to produce precipitation. The clouds have been mistaken for UFOs (or "visual cover" for UFOs), particularly the round "flying saucer"-type, 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 have never seen one and are not aware clouds with that shape can exist. Bright colors (called irisation) are sometimes seen along the edge of lenticular clouds.[1] 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.[2]

Altocumulus lenticularis Gallery

  • Dramatic "saucer cloud" over Campbell Mesa, Flagstaff, Arizona.

  • Lenticular above Funchal, Madeira, Portugal.

  • Lenticular cloud above Reno, Nevada, United States.

  • Lenticular cloud above Reno, Nevada, United States.

  • Lenticular clouds flying over Mount Hood in Oregon.

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

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

  • Lenticular cloud above northern Presidential Range, New Hampshire, United States.

  • Stratocumulus lenticularis clouds near Homer, Alaska, United States.

  • Stratocumulus lenticularis forming at the top of Mount Mikeno in the Democratic Republic of Congo.

  • Lenticular cloud above Skaftafell glacier in Iceland.

  • Lenticular Cloud over Santa Clarita, CA, United States.

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

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

  • Lenticular Clouds over Mount Hotaka, Hida Mountains in Nagano Prefecture, Japan.

  • Lenticular cloud over Saddleback Mountain, Orange County, California on September 7, 2014.

  • Lenticular cloud in Baguia, East Timor

  • Standing Jellyfish-Shaped Lenticular. Taken during a Lenticular outbreak on December 11, 2014, Wasatch Mountains, United States.

  • Stratocumulus lenticularis over Großer Rachel in Bohemian Forest, Germany/Czech Republic

  • A 30-second time-lapse video of a lenticular cloud generated by lee wave from winds flowing over Longs Peak, Colorado, United States.

See also

References

  1. ↑ Answers.com – Sci-Tech Dictionary:irisation
  2. ↑ FAI web site of world gliding records

External links

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