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Weird, Rare Clouds and the Physics Behind Them

Sometimes likened to UFOs, lenticular clouds are usually created by gravity waves. Chuang evokes loose shock absorbers to describe what gravity waves are.

“You take your grandma’s Cadillac and drive it over a speed bump, and after that it goes up and down for a while,” he said. “The reason you are going down is because of gravity, and then there are springs in the suspension that push you back up.”

In the case of lenticular clouds, the speed bump is usually some kind of topography, like a mountain, that gets in the way of air flow. As the air comes down the side of the mountain, it tends to overshoot and then springs back up. It oscillates like this for a while, and on the upward part of the waves, clouds form as rising air cools.

“Clouds mark the highest part of the oscillation,” Chuang said.

Lenticular clouds can also be caused by other speed bumps, such as tall thunderclouds, but because they often form on the downwind sides of mountains, they are also known as lee clouds, wave clouds or lee wave clouds.

A mountain range can form a series of long wave clouds, but if the speed bump is more isolated, like a single mountain, the result can be oval-shaped clouds that look like UFOs. Sometimes multiple ovals form that look like a stack of saucers.

Photo Credit: (1) cardiffjackie, (2) Daniel Breed. (3) Betsy Mason, Wired.com. (4)NCAR/UCAR.