Clouds (meteorology)

In meteorology, a cloud is an aerosol comprising a visible mass of minute liquid droplets, frozen crystals, or particles suspended in the atmosphere above the surface of a planetary body. The droplets and crystals may be made of water or various chemicals. On Earth, clouds are formed as a result of saturation of the air when it is cooled to its dew point, or when it gains sufficient moisture (usually in the form of water vapor) from an adjacent source to raise the dew point to the ambient temperature. They are seen in the Earth's homosphere (which includes the troposphere, stratosphere, and mesosphere). Nephology is the science of clouds which is undertaken in the cloud physics branch of meteorology.

There are two systems of naming clouds in their respective layers of the atmosphere; Latin in the troposphere and mostly alpha-numeric above the troposphere. Cloud types in the troposphere, the atmospheric layer closest to Earth's surface, have Latin names due to the universal adaptation of Luke Howard's nomenclature. Formally proposed in 1802, it became the basis of a modern international system that classifies clouds into five physical forms and three altitude levels (formerly known as étages). These physical types, in approximate ascending order of convective activity, include stratiform sheets, cirriform wisps and patches, stratocumuliform layers (mainly structured as rolls, ripples, and patches), cumuliform heaps, and very large cumulonimbiform heaps that often show complex structure. The physical forms are cross-classified by the altitude levels to produce ten basic genus-types, most of which can be divided into species, and subdivided into varieties.

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