WAVE CLOUDS

When air is lofted over a mountain range, it cools, saturates and condenses a winward-side cloud. The air surmounting the summit is just about at saturation, sometimes with respect to ice and at other times with respect to water, depending on the temperature and the height of the mountain barrier.

Forcing air up over the overlying atmosphere causes a spring-like rebound and so the air stream downwind from the mountain barrier often undergoes an undulatory wave-like motion. At the crest of such waves, the airmass is supersaturated and a 'wave-cloud' condenses out: In this example the wave cloud appear as flying saucers over Buttes on the Tanana Flats which are in mirage

Here are another couple examples of wave clouds: