Lenticular clouds (, ) are stationary

cloud In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles, suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may ...

s that form mostly in the

troposphere The troposphere is the lowest layer of the atmosphere of Earth. It contains 80% of the total mass of the Atmosphere, planetary atmosphere and 99% of the total mass of water vapor and aerosols, and is where most weather phenomena occur. From the ...

, typically in parallel alignment to the

wind direction Wind direction is generally reported by the direction from which the wind originates. For example, a ''north'' or ''northerly'' wind blows from the north to the south; the exceptions are onshore winds (blowing onto the shore from the water) and ...

. They are often comparable in appearance to a

lens A lens is a transmissive optical device that 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'') ...

or saucer. Nacreous clouds that form in the lower

stratosphere The stratosphere () is the second-lowest layer of the atmosphere of Earth, located above the troposphere and below the mesosphere. The stratosphere is composed of stratified temperature zones, with the warmer layers of air located higher ...

sometimes have lenticular shapes. There are three main types of lenticular clouds:

altocumulus Altocumulus () is a middle-altitude cloud genus that belongs mainly to the physical category, characterized by globular masses or rolls in layers or patchesthe individual elements being larger and darker than those of cirrocumulus and smaller t ...

standing lenticular (ACSL), stratocumulus standing lenticular (SCSL), and

cirrocumulus Cirrocumulus is one of the three main genus types of high-altitude tropospheric clouds, the other two being cirrus and cirrostratus. They usually occur at an altitude of , however they can occur as low as in the arctic and weather reporting sta ...

standing lenticular (CCSL), varying in altitude above the ground.

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 In physics, a standing wave, also known as a stationary wave, is a wave that oscillates in time but whose peak amplitude profile does not move in space. The peak amplitude of the wave oscillations at any point in space is constant with respect t ...

form on the

leeward In geography and seamanship, windward () and leeward () are directions relative to 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 o ...

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

dew point The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to produce a relative humidity of 100%. This temperature depends on the pressure and water content of the air. When the air at a temperature above the ...

, 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". 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 from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

. Lenticular clouds have been said to be mistaken for UFOs, 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 gradually to change colour as the angle of view or the angle of illumination changes. Iridescence is caused by wave interference of light in microstru ...

) 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 (over 22,000 metres; 74,334 ft) 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