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Amazing Cloud Pictures Definition

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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 in their most basic forms 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 to express variations or complexities in these basic forms or to specify middle or high altitude ranges. These include strato- for low clouds with limited convection that form mostly in uneven layers, cumulo- for complex highly-convective storm clouds, nimbo- for thick layered clouds of some complexity that can produce moderate to heavy precipitation, alto- for middle clouds, and cirro- for high clouds; the latter two of which may be of simple or moderately complex structure. 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.
Adiabatic cooling

All weather-related clouds form in the troposphere, the lowest layer of Earth's atmosphere. This generally happens when one or more lifting agents causes air containing invisible water vapor to rise and cool to its dew point, the temperature at which the air becomes saturated. The main mechanism behind this process is adiabatic cooling.[1] Atmospheric pressure decreases with altitude, so the rising air expands in a process that expends energy and causes the air to cool, which reduces its capacity to hold water vapor. If the air is cooled to its dew point and becomes saturated, it normally sheds vapor it can no longer retain which condenses into cloud.
Lifted condensation level

The altitude at which this begins to happen is called the lifted condensation level, which roughly determines the height of the cloud base.[1] Water vapor in saturated air is normally attracted to condensation nuclei such as salt particles that are small enough to be held aloft by normal circulation of the air. If the condensation process occurs below the freezing level in the troposphere, the nuclei help transform the vapor into very small water droplets. The average size of a newly formed droplet is around 0.02 mm (0.0008 in). High clouds that form above the freezing level are composed mostly of ice crystals. An absence of sufficient condensation particles at and above the condensation level causes the rising air to become supersaturated and the formation of cloud tends to be inhibited.
Frontal and cyclonic lift

There are three main agents of vertical lift. One comprises two closely related processes which work together. Frontal lift and cyclonic lift occur when stable or slightly unstable air, which has been subjected to little or no surface heating, is forced aloft at weather fronts and around centers of low pressure. Cloud droplets form when the air is lifted beyond the condensation level where water vapor condenses on so-called nuclei; (small particles) that grow to a size of typically 0.02 mm (.001 in). In a cloud the droplets collide to form larger droplets. These larger droplets remain aloft as long as the drag force of the air dominates over the gravitational force for small particles. If the cloud droplets continue to grow past this size, they become too heavy to be held aloft as the gravitational force overcomes the atmospheric drag, and they fall from the cloud as rain.[2] When this process takes place just above the freezing level, the vapor tends to condense into supercooled water droplets, which with additional lifting and growth in size, can eventually turn into freezing rain. At temperatures well below freezing, the vapor desublimates into ice crystals that average about 0.25 mm in length.[3] Continuing lift and desublimation will tend to increase the number of ice crystals which may combine until they are too heavy to be supported by the vertical air currents and fall out as snow.