weather [clouds]

CLOUDS [ANIMATIONS]

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CLOUDS [TYPES]

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CIRRUS

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CUMULUS

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STRATUS

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A classification of clouds was introduced by Luke Howard (1772-1864) who used Latin words to describe their characteristics. <br> Cirrus - a tuft or filament (e.g. of hair)<br> Cumulus - a heap or pile<br> Stratus - a layer<br> Nimbus - rain bearing<br> The basis of the naming convention he developed, which we still largely use today, is whether the clouds are at :<br> LOW altitudes (cumulus or stratus),<br> MEDIUM altitudes (alto),<br> HIGH altitudes (cirrus or cirro). <br> Most of the names are also based on whether they are :<br> lumpy in appearance (cumuloform) or <br> flat (stratiform).<br> nimbus (rain-bearing),<br> castellanus (castle-like),<br> lenticularis (lens-shaped)<br> Clouds form when moist air is cooled to such an extent it becomes saturated.<br> The main mechanism for cooling air is to force it to rise. <br> As air rises it expands - because the pressure decreases with height in the atmosphere - and this causes it to cool.<br> Eventually it may become saturated and the water vapour then condenses into tiny water droplets, similar in size to those found in fog, and forms cloud. <br> If the temperature falls below about minus 20 °C, many of the cloud droplets will have frozen so that the cloud is mainly composed of ice crystals.<br> The ten main types of cloud can be separated into three broad categories according to the height of their base above the ground: high clouds, medium clouds and low clouds.<br> High clouds<br> High clouds are usually composed solely of ice crystals and have a base between 5,500 and 14,000 metres.<br> Cirrus - white filaments<br> Cirrocumulus - small rippled elements<br> Cirrostratus - transparent sheet, often with a halo<br> Medium clouds<br> Medium clouds are usually composed of water droplets or a mixture of water droplets and ice crystals, and have a base between 2,000 and 5,500 metres.<br> Altocumulus - layered, rippled elements, generally white with some shading<br> Altostratus - thin layer, grey, allows sun to appear as if through ground glass<br> Nimbostratus - thick layer, low base, dark. Rain or snow falling from it may sometimes be heavy<br> Low clouds<br> Low clouds are usually composed of water droplets - though cumulonimbus clouds include ice crystals - and have a base below 2,000 metres. Stratocumulus - layered, series of rounded rolls, generally white with some shading<br> Stratus - layered, uniform base, grey<br> Cumulus - individual cells, vertical rolls or towers, flat base<br> Cumulonimbus - large cauliflower-shaped towers, often 'anvil tops', sometimes giving thunderstorms or showers of rain or snow<br>

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CIRRUS

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CUMULUS

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STRATUS

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