A pileus, also called scarf cloud or cap cloud, is a small, horizontal, lenticular cloud that can appear above a cumulus or cumulonimbus cloud, giving the parent cloud a characteristic "hoodlike" appearance. Pilei tend to change shape rapidly. They are formed by strong updraft at lower altitudes, acting upon moist air above, causing the air to cool to its dew point. As such, they are usually indicators of severe weather, and a pileus found atop a cumulus cloud often foreshadows transformation into a cumulonimbus cloud, as it indicates a strong updraft within the cloud. Read more ...
a stratovolcano covering almost the entirety of Matua Island in the Kuril Islands, Russia.
A Rainbow Pileus Cloud over ZimbabweFebruary 19, 2014
Image Credit & Copyright: Peter Lowenstein
Yes, but how many dark clouds have a multicolored lining? Pictured, behind this darker cloud, is a pileus iridescent cloud, a group of water droplets that have a uniformly similar size and so together diffract different colors of sunlight by different amounts. The above image was taken just before sunset when it was noticed by chance by a photographer in Murambi East, near Odzi Valley and the Mtanda Range of Zimbabwe. Also captured were unusual cloud ripples above the pileus cloud. The formation of a rare pileus cloud capping a common cumulus cloud is an indication that the lower cloud is expanding upward and might well develop into a storm. In this case, however, only a few minutes after the colorful cloud was noticed, it disappeared.
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