These undulating bands of Altocumulus lenticularis were striking enough to cause Dae-Am Yi (Member 64,103) to pull off the road near Eumseong, Chungcheongbuk-do, South Korea to appreciate them. The clouds reduced the bright morning Sun to a flat disc, forming pearly iridescence as they diffracted the sunlight.

Lenticularis clouds reveal otherwise invisible wavelike air movements that are caused by uneven terrain many miles upwind. Where the airflow rises and cools enough to reach the dew point, cloud develops. Where it dips and warms enough to dissipate the cloud droplets, gaps open up. The wind was strong enough here to tear feathery strands from the edges of Dae-Am’s clouds, but the clouds themselves would have remained largely fixed in place. Clouds of this lenticularis form remain fixed in place so long as the wind is steady. They’re like standing waves downstream of rocks on a fast-flowing river.