Cloud

In meteorology, a cloud is a visible mass of liquid droplets or frozen crystals made of water or various chemicals suspended in the atmosphere above the surface of a planetary body. These suspended particles are also known as aerosols. Clouds in earth's atmosphere are studied in the cloud physics branch of meteorology. Two processes, possibly acting together, can lead to air becoming saturated; cooling the air or adding water vapor to the air. In general, precipitation will fall to the surface; an exception is virga, which evaporates before reaching the surface.

The international cloud classification system is based on the fact clouds can show free-convective upward growth like cumulus, appear in non-convective layered sheets such as stratus, or take the form of thin fibrous wisps, as in the case of cirrus. Prefixes are used in connection with clouds: strato- for low clouds with limited convection that form mostly in layers, nimbo- for thick layered clouds that can produce moderate to heavy precipitation, alto- for middle clouds, and cirro- for high clouds. Whether or not a cloud is low, middle, or high level depends on how far above the ground its base forms. Cloud types with significant vertical extent can form in the low or middle altitude ranges depending on the moisture content of the air. Clouds in the troposphere have Latin names due to the popular adaptation of Luke Howard's cloud categorization system, which began to spread in popularity during December 1802. Synoptic surface weather observations use code numbers to record and report the types of tropospheric cloud visible at each scheduled observation time based on the height and physical appearance of the clouds.

While a majority of clouds form in Earth's troposphere, there are occasions when clouds in the stratosphere and mesosphere can be observed. These three main layers of the atmosphere where clouds may be seen are collectively known as the homosphere. Above this lies the thermosphere and exosphere, which together make up the heterosphere that marks the transition to outer space. Clouds have been observed on other planets and moons within the Solar System, but, due to their different temperature characteristics, they are composed of other substances such as methane, ammonia, and sulfuric acid.

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Other articles related to "cloud, clouds":

Jeans Instability - Jeans Length
... Jeans' length is the critical radius of a cloud (typically a cloud of interstellar dust) where thermal energy, which causes the cloud to expand, is counteracted by gravity ... Length is where is Boltzmann's constant, is the temperature of the cloud, is the radius of the cloud, is the mass per particle in the cloud, is the Gravitational ... the cloud's mass divided by the cloud's volume) ...
Entrainment (meteorology)
... air into a preexisting air current or cloud so that the environmental air becomes part of the current or cloud ... The entrainment coefficient in clouds is one of the most sensitive variables causing uncertainty in climate models ... assumes that the timescale for the mixing within a cloud was large compared to the condensation timescale ...
Preston Cloud - Professional Career
... Cloud's professional career alternated between the United States Geological Survey (where he was chief paleontologist from 1949-1959) and academia (Missouri ... While at UCSB he founded that institution's Preston Cloud Research Laboratory, originally dedicated to paleomicrobiology and to studies of the first lunar geological samples from the Apollo 11 space mission ... Cloud was a member of the National Academy of Sciences for thirty years, he was chairman of the Geology Section and occupied positions in its Council and ...
Cloud - Extraterrestrial
... planet or moon with an atmosphere also has clouds ... Venus's thick clouds are composed of sulfur dioxide ... Mars has high, thin clouds of water ice ...
Cloud Nine
... Cloud nine or on cloud nine is an idiom referring to a state of elation or happiness ... It may also refer to ...

Famous quotes containing the word cloud:

    The cloud was so dark that it needed all the bright lights that could be turned upon it. But for four years there was a contagion of nobility in the land, and the best blood North and South poured itself out a libation to propitiate the deities of Truth and Justice. The great sin of slavery was washed out, but at what a cost!
    M. E. W. Sherwood (1826–1903)

    A brush had left a crooked stroke
    Of what was either cloud or smoke
    From north to south across the blue;
    A piercing little star was through.
    Robert Frost (1874–1963)

    Hearing the low sound
    of a cloud scattering rain
    at midnight
    and thinking for an eternity
    on his absent young wife,
    a traveller heaved a sigh
    and with a flood of tears
    howled the whole night long.
    Now, villagers won’t let him stay
    in their place anymore.
    Amaru (c. seventh century A.D.)