Aliens aloft

They look like flying saucers. Some conspiracy theorists think they are flying saucers.

Entire websites are devoted to photographs and musings on lenticular, or lens-shaped, clouds. They appear in paintings and murals dating back centuries. Rounded and concave, lenticular clouds form over mountaintops -- such as Mt. Ruapehu in New Zealand, above; Mt. Rainier in Washington, top right; and a high point in Volcano, Hawaii, bottom right -- and seem to hover there for hours and sometimes days. “Picture the waves in the ocean,” says Andy Nash, science and operations officer for the National Weather Service in Honolulu. “The air has a lot of these waves, and most of the time you can’t see them. When you get the right combination of moisture and temperature, though, as the air rises on one of these waves, the clouds will form.”

Clouds of all kinds form when air is cooled until the water vapor that it contains condenses. Add in the sweep and surge of air currents as they hit and crest over mountaintops, and you’ve got the makings of a lenticular cloud.

As other clouds in the sky sail by, a lenticular cloud seems to stand still. What’s really happening is that the cloud is rapidly forming on one side and just as rapidly dispersing on the other. The cloud will last as long as the flow of moisture continues. Lenticular clouds often will be the only clouds in an otherwise clear, blue sky. “They form in really stable air that would otherwise not create clouds,” Nash says. “That’s why they often have a smooth and rounded shape and take on almost otherworldly forms. It really grabs people’s attention because the cloud forms and just seems to sit there.”