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List of cloud types
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Clouds are formed in Earth's atmosphere when water evaporates into vapor from oceans, lakes, ponds, and even streams and rivers; or by evapotranspiration over moist areas of Earth's land surface. The vapor rises up into colder areas of the atmosphere due to convective, orographic, or frontal lifting. The water vapor attaches itself to condensation nuclei which could be anything from dust to microscopic particles of salt and debris. Once the vapor has been cooled to saturation, the cloud becomes visible. All weather-producing clouds form in the troposphere, the lowest major layer of the atmosphere. However very small amounts of water vapor can be found higher up in the stratosphere and mesosphere and may condense into very thin clouds if the air temperatures are sufficiently cold. One branch of meteorology is focused on the study of nephology or cloud physics.Tropospheric clouds can be divided into three main categories with names based on Latin root words that indicate physical structure and process of formation. Clouds of the cirriform category are generally thin and occur mostly in the form of filaments. The other two categories are stratiform with clouds that are mostly sheet-like in structure, and cumuliform that appear heaped, rolled, and/or rippled.In the troposphere, nine of the ten genus types are derived by cross-classifying the three physical categories into four families defined by altitude range; high, middle, low, and moderate vertical. Each of these families includes one stratiform and one cumuliform genus. Cirriform clouds differ in that they are only found in the high altitude family as a third member, and therefore only constitute a single genus cirrus. High stratiform and cumuliform clouds carry the prefix cirro- which yield the genera cirrostratus and cirrocumulus. Middle cloud genera have the prefix alto- (altostratus and altocumulus) to distinguish them from the high clouds, while low altitude stratiform and cumuliform genera (stratus and stratocumulus) carry no height-related prefixes. The fourth family comprises stratiform and cumuliform genera of moderate vertical extent (nimbostratus and cumulus) that form in the low or middle altitude range. This group also has no height-related prefixes, but its stratiform genus carries the prefix nimbo- to denote its ability to produce widespread precipitation.A fifth family or sub-family of towering vertical clouds comprises only cumuliform types. One is cumulonimbus, the tenth genus type, and the other is cumulus congestus, a towering species of the genus cumulus whose other species belong to the family of moderate vertical clouds. All cloud genera except nimbostratus are divided into species and/or varieties based on specific physical characteristics of the clouds, but the cumulus genus is the only one that has species in two different altitude families. The essentials of the modern nomenclature system for tropospheric clouds were proposed by Luke Howard, a British manufacturing chemist and an amateur meteorologist with broad interests in science, in an 1802 presentation to the Askesian Society. Since 1890, clouds are classified and illustrated in cloud atlases.Clouds that form above the troposphere have a generally cirriform structure, but are not given Latin names based on that characteristic. Polar stratospheric clouds form at very high altitudes in polar regions of the stratosphere. They are given the name nacreous due to the mother-of-pearl colors that are typically seen, and are sub-classified alpha-numerically according to their chemical makeup. Polar mesospheric clouds are the highest in the atmosphere and are given the Latin name noctilucent which refers to their illumination during deep twilight. They are sub-classified alpha-numerically according to specific details of their cirriform physical structure.Mesospheric, stratospheric, and tropospheric classes are listed on this page in descending order of altitude. Within the troposphere, families of non-vertical clouds are also listed in descending order of altitude. The genus types within each family are arranged in descending order of average cloud base height. Their constituent species, varieties, and supplementary features are arranged in approximate order of frequency of occurrence. Families of vertical clouds and their constituent genera and species are listed in ascending order of average altitude of cloud tops. Varieties and supplementary features are arranged in order of approximate frequency of occurance.
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