Have you ever seen clouds seem to stand still while all the others around them are moving rapidly? Mountains in the West make these types of clouds fairly common. And, Arizona's mountains do a fantastic job at creating them.
Figure 1: Standing wave clouds
For an animation of standing wave clouds, simply click on the video attached to this story.
Standing wave clouds form when wind blows over a mountain. Since the wind can't possibly go INTO the mountain, it is forced up and over it.
When are rises, if it has enough moisture in it, the water vapor is condensed into visible cloud droplets. Thus, a cloud will form over or just downwind from the mountain.
Then, since the air was forced upward over the mountain, it undulates, or goes up and down as it moves on.
Each place it's going up, a cloud forms. The opposite is true when the air is going down in the undulation.
Voila: Standing wave clouds.
Figure 2: How standing waves form.
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