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.
Clouds can show convective development like cumulus,
appear in 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 cumuliform-category clouds that
show some stratiform characteristics, nimbo- for
thick stratiform 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 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
for 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 where clouds in the stratosphere
and mesosphere are observed. These three main layers
of the atmosphere where clouds may be seen are collectively
known as the homosphere. Above this lie 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.
(Source: Wikipedia.org)
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