Pileus (cloud)

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Clouds : classification
Genera species Subspecies

Special forms

Cumulonimbus with pileus over Lake Constance

Pileus ( Latin "cap", abbreviation pil ) is an accompanying cloud of small horizontal extent in the form of a cap or hood over the cloud top or directly on the upper part of a cumulus-like cloud , by which it is often pierced. Pilei tend to change their appearance very quickly. They arise when the air at the top of the cumulus is very humid and is lifted by the cloud, which continues to swell. They can be seen as precursors of a transformation of cumulus into cumulonimbus clouds and thus signal the possible formation of showers or thunderstorms. Pilei only occur with these two types of cloud and can often be observed on top of each other. They also occur during volcanic eruptions .

Development of a pileus in pictures

Web links

Pilei girding and crowning a cumulonimbus, so to speak
Commons : Pileus  - album with pictures, videos and audio files