A cloud is a visible mass of droplets A drop or straw is a small volume of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the lower end of a tube or other surface boundary, producing a hanging drop called a pendant drop. Drops may also be formed by the condensation of a vapor or by atomization of a larger mass of liquid of water or frozen crystals A crystal or crystalline solid is a solid material, whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is crystallography. The process of crystal formation via mechanisms of crystal growth is called suspended in the atmosphere An atmosphere is a layer of gases that may surround a material body of sufficient mass,and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low. Some planets consist mainly of various gases, but only their outer layer is their above the surface of the Earth Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet,[note 6] or by its Latin name, Terra.[note 7] or another planetary A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.[a] body. A cloud is also a visible mass attracted by gravity, such as masses of material in space called interstellar clouds Interstellar cloud is the generic name given to an accumulation of gas, plasma and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium. Depending on the density, size and temperature of a given cloud, the hydrogen in it can be neutral , ionized (H II regions) (ie. a and nebulae A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases. Originally nebula was a general name for any extended astronomical object, including galaxies beyond the Milky Way (some examples of the older usage survive; for example, the Andromeda Galaxy was referred to as the Andromeda Nebula before galaxies were. Clouds are studied in the nephology Nephology is the study of clouds and cloud formation. British meteorologist Luke Howard was a major researcher within this field, establishing a cloud classification system or cloud physics Cloud physics is the study of the physical processes that lead to the formation, growth and precipitation of clouds. Clouds are composed of microscopic droplets of liquid water , tiny crystals of ice (cold clouds), or both (mixed phase clouds). Under suitable conditions, the droplets combine to form precipitation, where they may fall to the earth branch of meteorology Meteorology is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and short term forecasting . Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the eighteenth century. The nineteenth century saw breakthroughs occur after observing networks developed.

On Earth the condensing substance is typically water vapor Water vapor or water vapour , also aqueous vapor, is the gas phase of water. Water vapor is one state of water within the hydrosphere. Water vapor can be produced from the evaporation of boiling liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously generated by evaporation and removed by, which forms small droplets or ice crystals Ice crystals are a small crystalline form of ice including hexagonal columns, hexagonal plates, dendritic crystals, and diamond dust, typically 0.01 mm (0.00039 in) in diameter. When surrounded by billions of other droplets or crystals they become visible as clouds. Dense deep clouds exhibit a high reflectance (70% to 95%) throughout the visible The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm. In terms of frequency, this corresponds to a band in the vicinity of 400-790 range of wavelengths. They thus appear white, at least from the top. Cloud droplets tend to scatter Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of reflected radiation from the angle predicted by the light efficiently, so that the intensity of the solar radiation Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon decreases with depth into the gases, hence the gray or even sometimes dark appearance at the cloud base This article refers to meteorology. For the airborne base of the TV series Captain Scarlet and the Mysterons, see Cloudbase. Thin clouds may appear to have acquired the color of their environment or background and clouds illuminated by non-white light, such as during sunrise or sunset, may appear colored accordingly. Clouds look darker in the near-infrared Infrared light is electromagnetic radiation with a wavelength between 0.7 and 300 micrometres, which equates to a frequency range between approximately 1 and 430 THz because water absorbs solar radiation at those wavelengths In physics, the wavelength of a sinusoidal wave is the spatial period of the wave – the distance over which the wave's shape repeats. It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a characteristic of both traveling waves and.

Contents

Classification

A cumulus cloudscape over Swifts Creek, Victoria Swifts Creek is a rural community located between Omeo and Ensay on the Great Alpine Road in East Gippsland, Victoria, Australia, 379 kilometres east of the state capital Melbourne. Swifts Creek is at an altitude of 300 m above sea level. The area was originally settled by Europeans in the gold rushes of the mid 1800s. At the 2006 census, Swifts, Australia

Cloud types or genera are grouped into three general categories: cirriform (wispy), stratiform (layered in sheets) and convective or cumuliform (heaped, rolled and/or rippled). These names distinguish a cloud's physical structure and process of formation. The individual genus types result from the categories being cross-classified by height range derived from the base height of the cloud, not the cloud top, and base height ranges may vary depending on the geographical zone Each of the five main latitude regions of the Earth's surface is said to be a geographical zone, divided by the major circles of latitude. The differences between them relate to climate, and the behaviour of the Sun. They are as follows:. This system was proposed in 1802, when it was presented to the Askesian Society The Askesian Society is a debating club for scientific thinkers, established in 1796 in London. The name was taken from the Greek term Askesis, meaning 'training' or 'application'. It was founded by William Allen, who allowed the use of his laboratory at No. 2 Plough Court for the Society's scientific experiments. The other two principal founders by Luke Howard Luke Howard was a British manufacturing chemist and an amateur meteorologist with broad interests in science. His lasting contribution to science is a nomenclature system for clouds, which he proposed in an 1802 presentation to the Askesian Society.

A sky of cirrus clouds.

High clouds (Family A)

High clouds will form between 10,000 and 25,000 ft (3,000 and 8,000 m) in the polar regions Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica. Polar sea ice is currently diminishing, possibly as a result of, 16,500 and 40,000 ft (5,000 and 12,000 m) in the temperate regions In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold. But in continental areas, such as central North America the variations between summer and winter can be extreme. In regions and 20,000 and 60,000 ft (6,000 and 18,000 m) in the tropical region the tropics are cold The tropics is a region of the Earth by the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately 23° 26′ 16″ N and the Tropic of Capricorn in the southern hemisphere at 23° 26′ 16″ ( or 23.438° ) S. The tropics are also referred to as the tropical zone and the torrid.[1]

Middle clouds (Family B)

Middle clouds tend to form at 6,500 ft (2,000 m) but may form at heights up to 13,000 ft (4,000 m), 23,000 ft (7,000 m) or 25,000 ft (8,000 m) depending on the region. Generally the warmer the climate, the higher the cloud base. Nimbostratus clouds A Nimbostratus cloud is characterized by a formless cloud layer that is almost uniformly dark gray. "Nimbo" is from the Latin word "nimbus", meaning rain. It is a stratiform cloud that produces rain, developing cloud bases between the surface and 10000 ft .[citation needed] Nimbostratus usually has a thickness of 2000 meters are sometimes included with the middle clouds.[1] The World Meterological Organization classifies Nimbostratus as a middle cloud that can thicken down into the low height range during precipitation.

Low clouds (Family C1)

Stratocumulus clouds, between Cumulus in the foreground and background

These are found from near surface up to 6,500 ft (2,000 m)[1] and include the stratus (dense and grey). When stratus clouds contact the ground, they are called fog Fog is a cloud that is in contact with the ground. A cloud may be considered partly fog; for example, the part of a cloud that is suspended in the air above the ground is not considered fog, whereas the part of the cloud that comes in contact with higher ground is considered fog.

Clouds in Family C1 include:

Low to middle clouds (Family C2)

These clouds can be based anywhere from near surface to about 10,000 ft (3,000 m). Cumulus usually forms in the low altitude range but bases may rise into the lower part of the middle range during conditions of very low relative humidity. Nimbostratus normally forms from altostratus in the middle altitude range but the base may subside into the low range during precipitaion.[2]

Clouds in Family C2 include:

Vertical clouds (Family D)

A typical anvil shaped Cumulonimbus incus

These clouds can have strong up-currents, rise far above their bases and form at many heights.

Clouds in Family D include:

Other clouds

A few clouds can be found above the troposphere The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and 99% of its water vapor and aerosols; these include noctilucent Noctilucent clouds, are tenuous cloud-like phenomena that are the "ragged-edge" of a much brighter and pervasive polar cloud layer called polar mesospheric clouds in the upper atmosphere, visible in a deep twilight. They are made of crystals of water ice. The name means roughly night shining in Latin. They are most commonly observed in and polar stratospheric clouds Polar stratospheric clouds , also known as nacreous clouds, are clouds in the winter polar stratosphere at altitudes of 15,000–25,000 meters (50,000–80,000 ft). They are implicated in the formation of ozone holes; their effects on ozone depletion arise because they support chemical reactions that produce active chlorine which catalyzes ozone (or nacreous clouds), which occur in the mesosphere The mesosphere is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. The mesosphere is located about 50 to 85 kilometers (30 to 50 miles) above the Earth's surface and stratosphere The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler higher up and warmer farther down. The border of the respectively.

Some clouds form as a consequence of interactions with specific geographical features. Perhaps the strangest geographically specific cloud in the world is Morning Glory, a rolling An arcus cloud is a low, horizontal cloud formation associated with the leading edge of thunderstorm outflow, or occasionally with a cold front even in the absence of thunderstorms. Roll clouds and shelf clouds are the two types of arcus clouds, slight variations in their generation and appearance being the difference cylindrical cloud which appears unpredictably over the Gulf of Carpentaria The Gulf of Carpentaria is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the Arafura Sea (the body of water that lies between Australia and New Guinea). The northern boundary is generally defined as a line from Slade Point (the northwestern corner of Cape York Peninsula) in the northeast to Cape in Northern Australia. Associated with a powerful "ripple" in the atmosphere, the cloud may be "surfed" in glider aircraft.

Cloud fields

A cloud field is simply a group of clouds but sometimes cloud fields can take on certain shapes that have their own characteristics and are specially classified. Stratocumulus clouds can often be found in the following forms:

Colors

Cloud iridescence occurring in clouds Sunset reflecting shades of grey and pink in clouds.

The color of a cloud, as seen from the Earth, tells much about what is going on inside the cloud. Clouds form because warm air tends to absorb water vapor, which is lighter than air, thus helping the mixture to rise. As it rises the air containing it cools and the vapor tends to condense out of the air as micro-droplets. These tiny particles of water are densely packed and sunlight cannot penetrate far into the cloud before it is reflected out, giving a cloud its characteristic white color. As a cloud matures, the dense water droplets may combine to produce larger droplets, which may combine to form droplets large enough to fall as rain. By this process of accumulation, the space between droplets becomes increasingly larger, permitting light to penetrate farther into the cloud. If the cloud is sufficiently large and the droplets within are spaced far enough apart, it may be that a percentage of the light which enters the cloud is not reflected back out before it is absorbed. A simple example of this is being able to see farther in heavy rain than in heavy fog. This process of reflection/absorption is what causes the range of cloud color from white to black. For the same reason, the undersides of large clouds and heavy overcasts can appear as various degrees of grey shades, depending on how much light is being reflected or transmitted back to the observer.

Other colors occur naturally in clouds. Bluish-grey is the result of light scattering within the cloud. In the visible spectrum, blue and green are at the short end of light's visible wavelengths, while red and yellow are at the long end. The short rays are more easily scattered by water droplets, and the long rays are more likely to be absorbed. The bluish color is evidence that such scattering is being produced by rain-sized droplets in the cloud.

A greenish tinge to a cloud is produced when sunlight is scattered by ice. A cumulonimbus cloud emitting green is an imminent sign of heavy rain, hail, strong winds and possible tornadoes.

Yellowish clouds are rare but may occur in the late spring through early fall months during forest fire season. The yellow color is due to the presence of pollutants in the smoke.

Red, orange and pink clouds occur almost entirely at sunrise/sunset and are the result of the scattering of sunlight by the atmosphere. The clouds do not become that color; they are reflecting long and unscattered rays of sunlight, which are predominant at those hours. The effect is much like if one were to shine a red spotlight on a white sheet. In combination with large, mature thunderheads this can produce blood-red clouds.

Clouds and climate

Global cloud cover, averaged over the month of October, 2009. The outlines of the continents can often be traced through observations of clouds alone, with the sharpest outlines where very dry land is surrounded by ocean. NASA composite satellite image; larger image available here. See also: Cloud cover and Cloud feedback

Understanding the role of clouds in regulating both weather and climate is at an early stage, and remains a critical unknown factor in predicting the extent of global warming.[citation needed]

Global brightening

New research indicates a global brightening trend.[6]

Global brightening is caused by decreased amounts of particulate matter in the atmosphere, leaving less surface area for condensation to occur. Less condensation in the atmosphere and more evaporation from increasing amounts of sunlight striking the surfaces of water causes more moisture to build in the air, creating fewer but more dense clouds.

Bacteria in clouds

Bacteria that live in clouds may have evolved the ability to promote rainstorms as a way to disperse themselves. These microbes—called ice nucleators—are found in rain, snow, and hail throughout the world, according to Brent Christner, a microbiologist at Louisiana State University. These bacteria may be part of a constant feedback between terrestrial ecosystems and clouds. They may rely on the rainfall to spread to new habitats, much as plants rely on windblown pollen grains, Christner said. [7]

Other planets

Main article: Extraterrestrial atmospheres

Within our Solar System, any planet or moon with an atmosphere also has clouds. Venus's clouds are composed of sulfuric acid droplets. Mars has high, thin clouds of water ice. Both Jupiter and Saturn have an outer cloud deck composed of ammonia clouds, an intermediate deck of ammonium hydrosulfide clouds and an inner deck of water clouds. Uranus and Neptune have cloudy atmospheres dominated by methane gas.

Saturn's moon Titan has clouds believed to be composed largely of droplets of liquid methane. The Cassini–Huygens Saturn mission uncovered evidence of a fluid cycle on Titan, including lakes near the poles and fluvial channels on the surface of the moon.

Gallery

Mixed clouds over Santa Clarita, CA.

In mountainous areas one often finds the peaks above the clouds as seen here with the Piz Bernina in the Swiss Alps.

Clouds and cloud bow above the Pacific Ocean.

Rain clouds over the North Sea taken from the coast of Herne Bay, Kent.

Rain clouds in Kerala, India.

Lenticular cloud over Wyoming.

The Space Shuttle Endeavour launches through some clouds.

Water clouds on Earth seen from space

See also

Weather portal

References

This article includes a list of references or external links, but its sources remain unclear because it has insufficient inline citations. Please help to improve this article by introducing more precise citations where appropriate. (September 2008)
  1. ^ a b c Cloud Classifications
  2. ^ Cite error: Invalid <ref> tag; no text was provided for refs named WMO_International_Cloud_Atlas; see Help:Cite errors/Cite error references no text
  3. ^ "Plymouth State Meteorology Program Cloud Boutique". http://vortex.plymouth.edu/clouds.html/.
  4. ^ "Cloud Types: common cloud classifications". WW2010. University of Illinois. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/home.rxml.
  5. ^ "cloud: Classification of Clouds". Infoplease.com. http://www.infoplease.com/ce6/weather/A0857400.html.
  6. ^ From Dimming to Brightening: Decadal Changes in Solar Radiation at Earth's Surface by Martin Wild et al. (Science 6 May 2005; 308: 847–850)
  7. ^ Rainmaking Bacteria Ride Clouds to "Colonize" Earth?

WMO International Cloud Atlas citation has been removed.

Bibliography

External links

Find more about Cloud on Wikipedia's sister projects:
Definitions from Wiktionary
Textbooks from Wikibooks
Quotations from Wikiquote
Source texts from Wikisource
Images and media from Commons
News stories from Wikinews
Learning resources from Wikiversity
Meteorological data and variables
General Adiabatic processes · Lapse rate · Lightning · Surface solar radiation · Surface weather analysis · Visibility · Vorticity · Wind
Condensation Cloud · Cloud condensation nuclei · Fog · Precipitation · Water vapor
Convection

Convective available potential energy (CAPE) · Convective inhibition (CIN) · Convective instability · Convective temperature (Tc) · Helicity · Lifted index (LI) · Bulk Richardson number (BRN)
Temperature Dew point (Td) · Equivalent temperature (Te) · Forest fire weather index · Haines Index · Heat index · Humidex · Humidity · Potential temperature (θ) · Equivalent potential temperature (θe) · Sea surface temperature (SST) · Wet-bulb temperature · Wet-bulb potential temperature · Wind chill
Pressure Atmospheric pressure · Baroclinity · Barotropicity
Cloud types
Extreme-level Nacreous · Noctilucent
High-level Cirrus (Ci) · Cirrus uncinus · Cirrus Kelvin-Helmholtz · Cirrostratus (Cs) · Cirrocumulus (Cc) · Cirrocumulus undulatus · Pileus · Contrail
Medium-level Altostratus (As) · Altostratus undulatus · Altocumulus (Ac) · Altocumulus undulatus · Altocumulus mackerel sky · Altocumulus castellanus · Altocumulus lenticularis
Low-level Fog · Stratus (St) · Cumulus (Cu) · Cumulus humilis (Cu) · Cumulus mediocris (Cu) · Stratocumulus (Sc) · Arcus (Roll) · Fractus · Funnel · Nimbostratus (Ns) · Nimbostratus virga · Shelf · Wall · Actinoform cloud · Undulatus asperatus
Vertical Cumulonimbus (Cb) · Cumulonimbus incus · Cumulonimbus calvus · Cumulonimbus mammatus · Cumulus congestus · Cumulus castellanus · Pyrocumulus · Pyrocumulonimbus · Overshooting top · Accessory

Categories: Clouds | Climate forcing agents

 

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