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A cirrocumulus is a type of cloud characterized by its high altitude and cottony appearance. Clouds are generally classified based on the height of their base, and cirrocumulus clouds are among the highest at 15 to 40 thousand feet(5 to 12 km) high. Cirrocumulus clouds take the form of sheets or patches composed of many tiny cloudlets arranged in rows, in what is sometimes described as a herringbone or mackerel pattern.
Like other cumulus clouds, cirrocumulus clouds form through convection. In this process, rising warm air reaches an area of relatively cooler air, causing the moisture in the air to condense into clouds. Cumulus clouds are characterized in appearance by well defined edges and a cottony look.
True cirrus clouds have the appearance of thin strands arranged in large sheets and consist only of ice crystals. Cirrocumulus clouds, on the other hand, contain mostly ice crystals along with some droplets of liquid water, though they are in a supercooled state, meaning that their temperature is below the freezing point, though they remain liquid. If all of the supercooled water droplets freeze rapidly, a cirrostratus cloud, consisting completely of ice crystals, will form.
Technically, each tiny cloudlet in the formation is a cirrocumulus cloud, but the term is commonly used to describe the aggregation of cloudlets into a large sheet. The larger cloud is typically white and fluffy in appearance, with no gray shadow. The clouds are usually short-lived and may produce a virga of ice or snow. A virga is a form of precipitation that can be seen falling from a cloud, but which melts and evaporates before reaching the ground.
Cirrocumulus clouds often appear together with other types of cumulus clouds, notably altocumulus clouds. Altocumulus cloudlets, however, are larger and darker in appearance. They also appear at a lower altitude, about 4,000 feet to 20,000 feet (1,200 to 6,100 meters), so they are not as cold as cirrocumulus clouds. Altocumulus clouds are either white or grey, and may signal the development of thunderstorms or rain.