Lee waves
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Image:LeeWaves.png In meteorology, Lee waves, also known as mountain waves, are periodic changes of pressure in a stream of air when the wind moves over mountains. This forces periodic changes in speed and direction of the air within this air stream. They always occur in groups on the lee side of mountains. Usually a horizontal turbulence is generated at the lee side of the first mountain (following the air stream), the so called rotor.
Both lee waves themselves as well as the rotor may be indicated by typical clouds which do not move with the wind as clouds usually do.
- At the vertex of the wave usually exists a cloud in shape of a lens (lenticularis).
- The rotor may generate a cumulus cloud in its raising part.
Frequently, a foehn wall cloud exists at the luv side of the mountains, however this is not a reliable indication of the presence of lee waves.
Lee waves provide a possibility for gliders to gain altitude when soaring. But especially the rotor may be harmfull for other small air crafts such as balloons, hang gliders and para gliders.