Clouds
Clouds are a large collection of minute water droplets and/or ice crystals that are suspended in the atmosphere. Two conditions are required for cloud masses to reach formation. Firstly, the air must be saturated. Secondly, condensation nuclei, that is, airborne dust or salt particles, must be present in substantial amounts, so that liquid droplets can form as the water vapour condenses.
As air parcels rise to higher, cooler atmospheric levels, condensation occurs. This is because cool air can not hold as much water vapour as warm air. The more moisture is present in the rising, cooling air, the greater the condensation will be, resulting in greater cloud formation. Most clouds form above the Earth's surface. However, when billions of tiny water droplets concentrate near the ground surface, fog is the result.
Cloud Classification
Clouds come in many shapes and sizes. They are grouped according to their form and the altitude at which they reside. The four families of cloud classification include the high, middle, and low clouds, as well as those with vertical development. Clouds are further categorized into two major classes according to their form. These include the stratiform clouds, layered in appearance covering large areas, and the cumuliform clouds which are globular in form.
High-level clouds include the cirrus, cirrocumulus and cirrostratus clouds. They form at altitudes above 20,000 feet and are typically composed of ice crystals. Mid-level clouds include the altocumulus and the altostratus forms, developing between 6,500 feet to 20,000 feet. Low-level clouds are found up to 6,500 feet. These include the stratus, nimbostratus and stratocumulus. Clouds with vertical development include the cumulus and the cumulonimbus clouds. The cumulonimbus clouds can reach heights far above their base and produce thunderstorms.
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