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Lenticulars
Thu Jun 17, 2004
Listen in RealAudio 
Have you ever seen a flying saucer? Well, if you look above a mountain on a windy day,
you might be surprised to see a massive grey-white disk floating over the summit.
Hi, I’m Bryan Yeaton for The Weather Notebook.
No, this is not an episode from the X Files, but a cloud: a lenticular cloud.
Lenticular, or to be technical, "altocumulus lenticularis," comes from the Latin root
meaning "lens-shaped." To get lenticular clouds, you need just the right conditions.
First, you must be near a mountainous area as the orographic effect, caused by the
shape of the mountains, causes the wind to undulate or form a wave. If the dew point
is at the right level, a cloud will form where the air cools as it rises on the upward
swing of the wave.
As the air is forced down on the other side, it is heated, and evaporates. The resulting
cloud usually looks like a big disk with a flat bottom. Actually, it looks a lot like a lentil.
Sometimes, several lenticulars can piggyback on each other, looking like a stack of
dinner plates. Although the lenticular can hover over an area for an hour or more, each
molecule is actually only traveling through, going from vapor to visible droplet and back
to vapor. The higher the wind, the sharper the edges of the cloud.
Lenticulars are also known as "cap clouds" as they are often found right over mountain
tops. However, depending on how the wave sets up, they can actually be a bit of a
distance from the actual summit—seeming like an alien ship scanning the forests and
valleys.
The Weather Notebook is funded by Subaru of America and the National Science
Foundation. We have lots of great pictures of lenticulars on our website:
www.weathernotebook.org. Check ‘em out!
Today's Links
Lenticular Cloud Photo 1
http://www.mountwashington.org/rotating/bryan_yeaton/lenticular.html
Lenticular Cloud Phtoto 2
http://www.mountwashington.org/photojournal/2003/01.html
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