Pileus is the name given to clouds that form a ‘cap’. The example below was taken by PWL chaser Daniel Pardini, 19th August 2013.
These caps are made of ice crystals high in the troposphere. They form as a parcel of air is shoved upward, in the shape of a dome or cap, just above a rapidly rising convective tower. In fact, pileus is the Latin word for cap. Moisture in the dome condenses directly into an ice fog as the air rises and cools, forming the pileus. Here is another example from PWL chaser Micheal Beazley, also taken on 19th August 3013.
Sometimes, the convection shoots right through the pileus layer, creating a ‘ring’ or ‘skirt’ effect.
image coming soon