Clouds are formed by the lifting of damp air, which cools by expansion as it encounters the lower pressures existing at higher levels in the atmosphere. The relative humidity increases until the air has become saturated with water vapour, and then condensation… Clouds are formed when relatively moist air rises. As a mass of air ascends, the lower pressures prevailing at higher levels allow it to expand.
Time-lapse video of clouds at sunset in Japan Etymology and history of cloud science and nomenclature[ edit ] Etymology[ edit ] The origin of the term cloud can be found in the old English clud or clod, meaning a hill or a mass of rock.
Around the beginning of the 13th century, the word came to be used as a metaphor for rain clouds, because of the similarity in appearance between a mass of rock and cumulus heap cloud.
Over time, the metaphoric usage of the word supplanted the old English weolcan, which had been the literal term for clouds in general. In about BC the Greek philosopher Aristotle wrote Meteorologicaa work which represented the sum of knowledge of the time about natural science, including weather and climate.
From that word came the modern term meteorologythe study of clouds and weather. Meteorologica was based on intuition and simple observation, but not on what is now considered the scientific method.
Nevertheless, it was the first known work that attempted to treat a broad range of meteorological topics. Howard was a methodical observer with a strong grounding in the Latin language and used his background to classify the various tropospheric cloud types during He believed that the changing cloud forms in the sky could What is the cloud the key to weather forecasting.
Lamarck had worked independently on cloud classification the same year and had come up with a different naming scheme that failed to make an impression even in his home country of France because it used unusual French names for cloud types.
His system of nomenclature included twelve categories of clouds, with such names as translated from French hazy clouds, dappled clouds and broom-like clouds.
By contrast, Howard used universally accepted Latin, which caught on quickly after it was published in How air becomes saturated[ edit ] Main article: Cloud physics Terrestrial clouds can be found throughout most of the homospherewhich includes the tropospherestratosphereand mesosphere.
Within these layers of the atmosphereair can become saturated as a result of being cooled to its dew point or by having moisture added from an adjacent source. The main mechanism behind this process is adiabatic cooling.
This condensation normally occurs on cloud condensation nuclei such as salt or dust particles that are small enough to be held aloft by normal circulation of the air.
However, if the air becomes sufficiently moist and unstable, orographic showers or thunderstorms may appear. Conductive, radiational, and evaporative cooling require no lifting mechanism and can cause condensation at surface level resulting in the formation of fog.
Water or moist ground,    precipitation or virga,  and transpiration from plants  Classification: How clouds are identified in the troposphere[ edit ] For a comprehensive listing of over 90 combinations of genera divided into species and subdivided into varieties with Latin etymologies, see List of cloud types.
Tropospheric classification is based on a hierarchy of categories with physical forms and altitude levels at the top. These forms are commonly used for the purpose of satellite analysis. Conversely, low stratiform cloud results when advection fog is lifted above surface level during breezy conditions.
Cirriform[ edit ] Cirriform clouds are generally of the genus cirrus and have the appearance of detached or semi-merged filaments.
They form at high tropospheric altitudes in air that is mostly stable with little or no convective activity, although denser patches may occasionally show buildups caused by limited high-level convection where the air is partly unstable.
In general, small cumuliform clouds tend to indicate comparatively weak instability. Larger cumuliform types are a sign of moderate to strong atmospheric instability and convective activity.
Atmospheric convection The largest free-convective clouds comprise the genus cumulonimbus which are multi-level because of their towering vertical extent. They occur in highly unstable air  and often have fuzzy outlines at the upper parts of the clouds that sometimes include anvil tops.
Weather map and Station model Genus classification and identification by altitude of occurrence.
Multi-level types not limited by altitude include the two main precipitating clouds, cumulonimbus and nimbostratus. The latter has been horizontally compressed in this depiction.cloud watching n noun: Refers to person, place, thing, quality, etc.
(observing clouds) osservazione delle nuvole nf: I enjoy cloud watching while lying on the grass in the park. Mi piace fare osservazione delle nuvole mentre sto disteso su un prato nel parco.
cloud [sb] 's judgment. Access Google Drive with a free Google account (for personal use) or G Suite account (for business use).
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