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[Stockbild] Lenticular cloud. Skier looks at a lenticular cloud or altocumulus lenticularis. These clouds get their name from their smooth, lens-like shape. They are usually caused when wind forms standing waves of air on the lee side of mountains. Lenti- cular clouds form when moisture in the air conden- ses at the top of these waves, and dissipate when the air descends again. The cloud pattern depends upon the wind speed and the shape of the mountains. A constant wind may produce clouds which are stable and remain virtually stationary in the sky for long periods. Lenticular clouds are sometimes mistaken for alien "flying saucer" spacecraft. Photographed from Mauna Kea, Hawaii, USA. (KEYSTONE/SCIENCE PHOTO LIBRARY/Folsom/Magrath) === === : DIA, Mittelformat, Nr. E120/453]