AskDefine | Define cloud

Dictionary Definition



1 any collection of particles (e.g., smoke or dust) or gases that is visible
2 a visible mass of water or ice particles suspended at a considerable altitude
3 out of touch with reality; "his head was in the clouds"
4 a cause of worry or gloom or trouble; "the only cloud on the horizon was the possibility of dissent by the French"
5 suspicion affecting your reputation; "after that mistake he was under a cloud"
6 a group of many insects; "a swarm of insects obscured the light"; "a cloud of butterflies" [syn: swarm]


1 make overcast or cloudy; "Fall weather often overcasts our beaches" [syn: overcast] [ant: clear up]
2 make less visible or unclear; "The stars are obscured by the clouds" [syn: obscure, befog, becloud, obnubilate, haze over, fog, mist]
3 billow up in the form of a cloud; "The smoke clouded above the houses"
4 make gloomy or depressed; "Their faces were clouded with sadness"
5 place under suspicion or cast doubt upon; "sully someone's reputation" [syn: defile, sully, corrupt, taint]
6 colour with streaks or blotches of different shades [syn: mottle, dapple]
7 make milky or dull; "The chemical clouded the liquid to which it was added"

User Contributed Dictionary






  1. A visible mass of water droplets suspended in the air.
  2. Any mass of dust, steam or smoke resembling such a mass.
  3. Anything which makes things foggy or gloomy.
  4. A group of objects, especially suspended above the ground or flying.
    He opened the door and was greeted by a cloud of bats.
visible mass of water droplets suspended in the air
mass of dust, steam or smoke
anything which makes things foggy or gloomy
group of objects suspended above the ground or flying
  • Finnish: pilvi, parvi
  • Japanese: 雲 (くも), 靄 (もや), 霧 (きり)
  • Portuguese: nuvem

See also


  1. To become foggy or gloomy, to become obscured from sight.
  2. To make obscure (e.g. to cloud the issue).


to become foggy or gloomy, to become obscured from sight
  • Finnish: samentua, sumentua, huurtua
to make obscure (e.g. to cloud the issue)
  • Finnish: sumentaa, sumentaa, hämärtää

Extensive Definition

A cloud is a visible mass of droplets or frozen crystals floating in the atmosphere above the surface of the Earth or another planetary body. A cloud is also a visible mass attracted by gravity (clouds can also occur as masses of material in interstellar space, where they are called interstellar clouds and nebulae.) The branch of meteorology in which clouds are studied is nephology.
On Earth the condensing substance is typically water vapor, which forms small droplets or ice crystals, typically 0.01 mm 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 range of wavelengths: they thus appear white, at least from the top. Cloud droplets tend to scatter light efficiently, so that the intensity of the solar radiation decreases with depth into the gases, hence the gray or even sometimes dark appearance of the clouds at their base. 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 be colored accordingly. In the near-infrared range, clouds would appear darker because the water that constitutes the cloud droplets strongly absorbs solar radiation at those wavelengths.
Clouds are divided into two general categories: layered and convective. These are named stratus clouds (or stratiform, the Latin stratus means "layer") and cumulus clouds (or cumuliform; cumulus means "piled up"). These two cloud types are divided into four more groups that distinguish the cloud's altitude. Clouds are classified by the cloud base height, not the cloud top. This system was proposed by Luke Howard in 1802 in a presentation to the Askesian Society.

High clouds (Family A)

These generally form above , in the cold region of the troposphere. In Polar regions, they may form as low as ; they are denoted by the prefix cirro- or cirrus. At this altitude, water frequently freezes so clouds are composed of ice crystals. The clouds tend to be wispy and are often transparent.
Clouds in Family A include:

Middle clouds (Family B)

These develop between 6,500 and 20,000 feet (between 2,000 and 6,000 m) and are denoted by the prefix alto-. They are made of water droplets and are frequently supercooled.

Low clouds (Family C)

These are found up to 6,500 feet (2,000 m) and include the stratus (dense and grey). When stratus clouds contact the ground, they are called fog.
Clouds in Family C include:

Vertical clouds (Family D)

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; these include noctilucent and polar stratospheric clouds (or nacreous clouds), which occur in the mesosphere and stratosphere 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 cylindrical cloud which appears unpredictably over the Gulf of Carpentaria in Northern Australia. Associated with a powerful "ripple" in the atmosphere, the cloud may be "surfed" in unpowered 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:
  • Open cell, which resembles a honeycomb, with clouds around the edges and clear, open space in the middle.
  • Closed cell, which is cloudy in the center and clear on the edges, similar to a filled honeycomb.
  • Actinoform, which resembles a leaf or a spoked wheel.


The color of a cloud tells much about what is going on inside the cloud. Clouds form when relatively warm air containing water vapor is lighter than its surrounding air and this causes it to rise. As it rises it cools and the vapor condenses out of the air as micro-droplets. These tiny particles of water are relatively 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 droplets may combine to produce larger droplets, which may combine to form droplets large enough to fall as rain. In this process of accumulation, the space between droplets becomes larger and larger, permitting light to penetrate much 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 (Think of how much farther one can see in a heavy rain as opposed to how far one can see in a heavy fog). This process of reflection/absorption is what leads to the range of cloud color from white through grey through black. For the same reason, the undersides of large clouds and heavy overcasts appear various degrees of grey; little light is being reflected or transmitted back to the observer.
Other colours 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 which shows 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 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 are not that color; they are reflecting the long (and unscattered) rays of sunlight which are predominant at those hours. The effect is much the same as if one were to shine a red spotlight on a white sheet. In combination with large, mature thunderheads this can produce blood-red clouds. The evening before the Edmonton, Alberta tornado in 1987, Edmontonians observed such clouds — deep black on their dark side and intense red on their sunward side. In this case the adage "red sky at night, sailor's delight" was wrong.The cloud was white because the reflection of the sun

Global dimming

The recently recognized phenomenon of global dimming is thought to be caused by changes to the reflectivity of clouds due to the increased presence of aerosols and other particulates in the atmosphere.

Global brightening

New research 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) indicates global brightening trend.
Global brightening is caused by decreased amounts of particulate matter in the atmosphere. With less particulate matter there is less surface area for condensation to occur. Since there's less condensation in the atmosphere and increased evaporation caused by increasing amounts of sunlight striking the water's surface there is more moisture, causing fewer but thicker clouds.

Clouds on other planets

Within our solar system, any planet or moon with an atmosphere also has clouds. Venus' clouds are composed entirely 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 atmospheres dominated by methane clouds.
Saturn's moon Titan has clouds which are believed to be composed largely of droplets of liquid methane. The Cassini-Huygens Saturn mission has uncovered evidence of a fluid cycle on Titan, including lakes near the poles and fluvial channels on the surface of the moon.


  • Hamblyn, Richard The Invention of Clouds — How an Amateur Meteorologist Forged the Language of the Skies Picador; Reprint edition (August 3, 2002). ISBN 0312420013
  • Could Reducing Global Dimming Mean a Hotter, Dryer World?


cloud in Arabic: سحاب
cloud in Aragonese: Boira
cloud in Official Aramaic (700-300 BCE): ܥܢܢܐ
cloud in Aymara: Qinaya
cloud in Min Nan: Hûn
cloud in Bosnian: Oblak
cloud in Breton: Koumoul
cloud in Bulgarian: Облак
cloud in Catalan: Núvol
cloud in Czech: Oblak
cloud in Corsican: Nivulu
cloud in Welsh: Cwmwl
cloud in Danish: Sky (meteorologi)
cloud in Pennsylvania German: Wolk
cloud in German: Wolke
cloud in Estonian: Pilv
cloud in Modern Greek (1453-): Νέφος
cloud in Emiliano-Romagnolo: Nóvvla
cloud in Spanish: Nube
cloud in Esperanto: Nubo
cloud in Basque: Hodei
cloud in Extremaduran: Nubi
cloud in Persian: ابر
cloud in French: Nuage
cloud in Friulian: Nûl
cloud in Scottish Gaelic: Neul
cloud in Galician: Nube
cloud in Korean: 구름
cloud in Hindi: बादल
cloud in Croatian: Oblaci
cloud in Indonesian: Awan
cloud in Inuktitut: ᓄᕗᔭᖅ/nuvujaq
cloud in Icelandic: Ský
cloud in Italian: Nuvola
cloud in Hebrew: ענן
cloud in Kurdish: Ewr
cloud in Latin: Nubes
cloud in Latvian: Mākoņi
cloud in Luxembourgish: Wollek
cloud in Lithuanian: Debesis
cloud in Hungarian: Felhő
cloud in Macedonian: Облак
cloud in Malayalam: മേഘം
cloud in Malay (macrolanguage): Awan
cloud in Dutch: Wolk
cloud in Cree: ᑲᔥᑰᐧᐃᓐ
cloud in Japanese: 雲
cloud in Norwegian: Sky
cloud in Norwegian Nynorsk: Sky
cloud in Narom: Nouage
cloud in Polish: Chmura
cloud in Portuguese: Nuvem
cloud in Romanian: Nor
cloud in Quechua: Phuyu
cloud in Russian: Облако
cloud in Sicilian: Nùvula
cloud in Simple English: Cloud
cloud in Slovak: Oblak
cloud in Slovenian: Oblak
cloud in Serbian: Облак
cloud in Serbo-Croatian: Oblak
cloud in Sundanese: Awan
cloud in Finnish: Pilvi
cloud in Swedish: Moln
cloud in Telugu: మేఘం
cloud in Thai: เมฆ
cloud in Vietnamese: Mây
cloud in Tajik: Абр
cloud in Cherokee: ᎤᎶᎩᎸ
cloud in Turkish: Bulut
cloud in Ukrainian: Хмари
cloud in Yiddish: וואלקן
cloud in Contenese: 雲
cloud in Samogitian: Debesis
cloud in Chinese: 云

Synonyms, Antonyms and Related Words

a mass of, a world of, addle, addle the wits, adumbrate, afterdamp, apply to, army, ball up, becloud, bedarken, bedazzle, bedim, befog, befuddle, befuddlement, begloom, bemist, besmear, besmirch, bevy, bewilder, bewilderment, black, black out, blackdamp, blacken, blanket, blind, block, block the light, blot out, blur, bother, botheration, breath, brown, bug, bunch, camouflage, canopy, cast a shadow, chaos, charm, chokedamp, clabber up, cloak, clothe, cloud, cloud over, cloud up, clutter, conceal, confuse, confusion, cope, cover, cover up, covey, cowl, crowd, curtain, damp, darken, darken over, daze, dazzle, dim, dim out, discolor, discombobulate, discombobulation, discomfit, discomfiture, discompose, discomposure, disconcert, disconcertion, disguise, disorder, disorganization, disorganize, disorient, disorientation, dissemble, distract, distract attention from, disturb, disturbance, eclipse, effluvium, embarrass, embarrassment, encloud, encompass with shadow, enmist, ensconce, enshroud, entangle, envelop, exhalation, fetid air, film, firedamp, flatus, flight, flock, flocks, fluid, flummox, flurry, fluster, flutter, fog, frenzy, fuddle, fuddlement, fume, fuss, gaggle, gloom, gloss over, hail, haze, hide, hive, hood, host, jam, jumble, keep under cover, large amount, lay on, lay over, legion, lots, malaria, mantle, many, mask, masses of, maze, mephitis, mess, miasma, mist, mix up, mob, moider, muchness, muddle, muddlement, muddy, muffle, multitude, murk, murmuration, nest, nubilate, numbers, obduce, obfuscate, obnubilate, obscure, obumbrate, occult, occultate, opaque, overcast, overcloud, overlay, overshadow, oversmoke, overspread, pack, perplex, perplexity, perturb, perturbation, plague, plurality, pother, pucker, puff of smoke, put on, put out, puzzle, quantities, quite a few, raise hell, rattle, reek, rout, ruck, ruffle, scores, screen, scum, shade, shadow, shield, shoal, shroud, shuffle, skein, slur over, smear, smog, smoke, smudge, somber, spread over, spring, steam, stew, sully, superimpose, superpose, swarm, sweat, swivet, tar, tarnish, throng, throw into confusion, tidy sum, tizzy, unsettle, unsettlement, upset, vapor, varnish, veil, volatile, watch, water vapor, whitewash, worlds of
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