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Altostratus undulatus cloud

earth science Maturity 5-7 Next article →

Some clouds look like wavy lines in the sky. This is the altostratus undulatus cloud. These clouds have wavy shapes called undulations. You might see wavy bottoms on the clouds. Often, you cannot see these waves with your eyes.

These clouds form in a special way. They appear when air moves in a set of steps. This happens during early stages of return flows. These flows are becoming unstable. You can find these clouds over the southern plains of the United States. They often show up when the ground is cool.

The wavy strips stay near an inversion surface. An inversion surface is a layer in the air. People use many names for these clouds. Some call them billow clouds. Others call them wind row clouds. You might also hear them called wave clouds. Sometimes, single waves stretch across the sky. Other times, many waves merge together. They make big patterns in the air.

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