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. Lenticular clouds sometimes form at the crests of these waves. Under certain conditions, long strings of lenticular clouds can form, creating a formation known as a wave cloud.
Power pilots tend to avoid flying near lenticular clouds because of the turbulence of the rotor systems that accompany them, but sailplane pilots actively seek them out. This is because the systems of atmospheric standing waves that cause "lennies" (as they are sometimes familiarly called) also involve large vertical air movements, and 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 3,000km) and altitude (14,938m) were set using such lift.
Lenticular clouds have been mistaken for UFOs (or "visual cover" for UFOs) because these clouds have a characteristic lens appearance and smooth saucer-like shape. Bright colors (called Irisation) are sometimes seen along the edge of lenticular clouds.[1] (http://en.wikipedia.org/wiki/Lenticular_cloud)
___________________________________________________________________________________
Lenticular Clouds Above Mt. Rainier in Washington State NASA - February 3, 2009
A Lenticular Cloud Over New Zealand NASA - January 21, 2009
Lenticular Clouds Over Mount Shasta
Taken by Photos by Kevin Lahey
Taken by Thedra
Taken by Peter K. - April 8, 2008 - Palm Desert, California
Taken by Stuart Anderson - August 3, 2006 - Saskatchewan, Canada
Taken by Joan Smith - Dec. 26, 2006 - in Sedona, Arizona
(còn tiếp)