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Clouds: A Summary

Clouds are visible masses of liquid droplets or frozen crystals suspended in the atmosphere.
They are formed as a result of saturation of the air when it is cooled to its dew point or gains sufficient moisture.
Clouds are seen in the Earth's homosphere, which includes the troposphere, stratosphere, and mesosphere.
There are two methods of naming clouds in their respective layers of the homosphere, Latin and common name.
Clouds can have a direct effect on climate change on Earth by reflecting incoming rays from the sun or trapping longer wave radiation.
Clouds formed above the troposphere are too scarce and too thin to have any influence on climate change.
Adiabatic cooling, frontal/cyclonic lift, and orographic lift cause a parcel of air containing invisible water vapor to rise and cool to its dew point.
Nonadiabatic cooling requires no lifting mechanism and can cause condensation at surface level resulting in the formation of fog.
Tropospheric clouds form in any of three levels based on altitude range above the Earth's surface.
High, mid-level, low, multi-level or moderate vertical and towering vertical are the five physical forms based on structure and process of formation.
Each altitude level comprises two or three genus-types differentiated mainly by physical form.
Multi-level clouds with significant vertical extent are separately listed and summarized.Cloud Types and Their Characteristics
Clouds are classified into ten basic types based on their height, shape, and composition.
Clouds are divided into three categories: low-level, middle-level, and high-level clouds.
High-level clouds are typically found above 20,000 feet and are thin and wispy in appearance.
Middle-level clouds are found between 6,500 and 20,000 feet and are usually composed of water droplets.
Low-level clouds are typically found below 6,500 feet and are composed of water droplets or ice crystals.
Clouds are further divided into genus types, which are based on their shape and height.
Genus types are divided into species, which indicate specific structural details that can vary according to atmospheric conditions.
Species are grouped into stable, ragged, partly unstable, and unstable categories.
Cloud varieties are further subdivisions of genus and species types and describe patterns or opacity of cloud structures.
Supplementary features and accessory clouds are not further subdivisions of cloud types but are precipitation or special cloud types that form in association with certain cloud genera, species, and varieties.
Supplementary features include precipitation-based and cloud-based features, while accessory clouds are typically ragged clouds of the genera and species cumulus fractus or stratus fractus.
A cloud's full technical name can include its genus, species, and combined varieties.Classification and Distribution of Tropospheric Clouds
Clouds form in clear air or when fog rises above surface level
Clouds are classified based on air mass characteristics such as stability and moisture content
Mother clouds retain their original form after the appearance of a new genus, genitus clouds, while mutatus clouds undergo a complete change in genus
Genitus and mutatus categories include types that do not originate from pre-existing clouds such as cumulus formed by large scale fires or volcanic eruptions
Clouds can be organized into patterns that cover large areas and are best seen from an aircraft or spacecraft
Stratocumulus clouds can be organized into fields that take on certain specially classified shapes and characteristics
Vortex streets are patterns that are formed from a phenomenon known as Kármán vortex and give clouds a twisted appearance
Cloud prevalence in the troposphere varies by latitude, being most prevalent in and along low pressure zones of surface tropospheric convergence close to the equator and near the 50th parallels of latitude in the northern and southern hemispheres
Divergence along high-pressure zones leads to the horizontal outflow of air from the upper part of a rising column of air, and cloudiness tends to be least prevalent near the poles and in the subtropics close to the 30th parallels
Clouds exert numerous influences on Earth's troposphere and climate, including being the source of precipitation, and they may promote cooling or warming of the Earth's surface
The complexity and diversity of clouds in the troposphere make it difficult to predict changes in cloud patterns and properties in a future, warmer climate
Polar stratospheric clouds are found in the lowest part of the stratosphere and are classified as a singular type with no differentiated altitude levels, genus types, species, or varieties.Noctilucent clouds are the highest clouds in the atmosphere, found at 80 to 85 km, and are given this name because of their illumination well after sunset and before sunrise.

Noctilucent clouds have four major types, including veils, bands, billows, and whirls, based on physical structure and appearance.

Their distribution tends to be restricted to polar regions of Earth, and sightings are rare more than 45 degrees south of the north pole or north of the south pole.

An increasing frequency of occurrence of noctilucent clouds since the 19th century may be the result of climate change.

Mesospheric convective lift during the polar summer can cause adiabatic cooling of small amounts of water vapor to the point of saturation, producing the coldest temperatures in the entire atmosphere just below the mesopause.

Smoke particles from burnt-up meteors provide much of the condensation nuclei required for the formation of noctilucent clouds.

Cloud cover has been seen on most other planets in the solar system, with Venus's thick clouds composed of sulfur dioxide and arranged in three main layers at altitudes of 45 to 65 km.

Both Jupiter and Saturn have an outer cirriform cloud deck composed of ammonia, and Titan has cirrus clouds believed to be composed largely of methane.

Clouds play an important mythical or non-scientific role in various cultures and religious traditions.

In China, clouds are symbols of luck and happiness, and overlapping clouds are thought to imply eternal happiness.

Informal cloud watching or cloud gazing is a popular children's activity involving watching the clouds and looking for shapes in them, a form of pareidolia.