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
The genitus and mutatus categories have been expanded to include certain types that do not originate from pre-existing clouds. The term "flammagenitus" (Latin for 'fire-made') applies to cumulus congestus or cumulonimbus that are formed by large scale fires or volcanic eruptions. Smaller low-level "pyrocumulus" or "fumulus" clouds formed by contained industrial activity are now classified as cumulus "homogenitus" (Latin for 'man-made'). Contrails formed from the exhaust of aircraft flying in the upper level of the troposphere can persist and spread into formations resembling any of the high cloud genus-types and are now officially designated as cirrus, cirrostratus, or cirrocumulus homogenitus. If a homogenitus cloud of one genus changes to another genus type, it is then termed a "homomutatus" cloud. Stratus cataractagenitus (Latin for 'cataract-made') are generated by the spray from waterfalls. "Silvagenitus" (Latin for 'forest-made') is a stratus cloud that forms as water vapor is added to the air above a forest canopy.