Cumulus cloud
Cumulus clouds are often precursors of other types of clouds, such as cumulonimbus, when influenced by weather factors such as instability, moisture, and temperature gradient. Normally, cumulus clouds produce little or no precipitation, but they can grow into the precipitation-bearing congestus or cumulonimbus clouds. Cumulus clouds can be formed from water vapor, supercooled water droplets, or ice crystals, depending upon the ambient temperature. They come in many distinct subforms, and generally cool the earth by reflecting the incoming solar radiation. Cumulus clouds are part of the larger category of free-convective cumuliform clouds, which include cumulonimbus clouds. The latter genus-type is sometimes categorized separately as cumulonimbiform due to its more complex structure that often includes a cirriform or anvil top. There are also cumuliform clouds of limited convection that comprise stratocumulus (low-étage), altocumulus (middle-étage) and cirrocumulus (high-étage). These last three genus-types are sometimes classified separately as stratocumuliform.
Cloud physics
Clouds in the troposphere, the atmospheric layer closest to Earth, are classified according to the height at which they are found, and their shape or appearance. There are five "forms" based on physical structure and process of formation. "Cirriform" clouds are high, thin and wispy, and are seen most extensively along the leading edges of organized weather disturbances. "Stratiform" clouds are non-convective and appear as extensive sheet-like layers, ranging from thin to very thick with considerable vertical development. They are mostly the product of large-scale lifting of stable air. Unstable free-convective "cumuliform" clouds are formed mostly into localized heaps. "Stratocumuliform" clouds of limited convection show a mix of cumuliform and stratiform characteristics which appear in the form of rolls or ripples. Highly convective "cumulonimbiform" clouds have complex structures often including cirriform tops and stratocumuliform accessory clouds.