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Meteorol a uniform layer of cloud above about 6000 metres (20 000 feet)
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
These clouds form typically as a thin whitish sheet covering a major portion of the sky. They may be very thin or form a definite sheet. They are responsible for forming halos around the sun and the moon. Cirrostratus clouds contain ice crystals or needles of ice. Some of the symbols for cirrostratus clouds on weather maps are and . The first symbol indicates that the amount of cirrostratus is not increasing, whereas the second symbol means that the sky is overcast with cirrostratus.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved