Dramatic lenticular cloud formation over Harold's Cross, Dublin
|Genus||Stratocumulus, altocumulus, cirrocumulus|
|Species||lenticularis (Latin: lens-shaped)|
|Altitude||up to 12,000 m
Lenticular clouds (Altocumulus lenticularis in Latin) are stationary clouds that form in the troposphere, typically in perpendicular alignment to the wind direction. They are often comparable in appearance to a lens or saucer.
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 appearance
As 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.
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.[nb 1] Bright colours (called iridescence) are sometimes seen along the edge of lenticular clouds.
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 to great distances. As of 2016[update] the gliding world records for both distance (over 3,000 km; 1,864 mi) and absolute altitude (15,460 m; 50,721 ft) were set using such lift.
- Pileus (meteorology), or cap cloud
- 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.
|Wikimedia Commons has media related to Lenticular cloud.|
- 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
- NASA Astronomy Picture of the Day: Picture of the Day 2009-01-21: A lenticular Cloud over New Zealand (21 January 2009)
- Sistek, Scott. "Mt. Rainier puts on a show!". KOMONews.com. Retrieved 2008-12-11.
- NASA Astronomy Picture of the Day: Lenticular Clouds near Mt. Ranier, Washington, USA (3 February 2009)
- San Francisco's Richmond District 2007: "Lennies" attacking the Richmond