- A uniform pattern of cloud billows fills this Altocumulus sheet
- W004098Z
- Cloud billows. A uniform billow pattern fills this Altocumulus cloud sheet with evenly spaced cloud rolls alternating with clear spaces. Air within the layer undulates as a set of waves pass through it. Lift in each wave crest condenses as cloud, while the troughs evaporate cloud. Small variations in horizontal flow disrupt the otherwise near perfect pattern.
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