Explain the differences between clouds that form at different levels.

Scientists often group clouds in groups of low clouds,
middle clouds and high clouds, according to their height above the ground at which they
form. A stratus cloud looks like a smooth, even sheet. A stratocumulus has light and
dark areas on the bottom, indicating presence of piles of clouds in the
layer.

The low clouds are are usually seen near the earth
surface, less than 1800 meters above the ground. These are further classified as stratus
and stratocumulus clouds according to their shape and
colour.

Middle clouds lie from 1800 to 6000metersabove the
earths surface. These are further classified as altostratus, altocumulus, and
nimbostratus clouds. An altostratus cloud forms a smooth white or grey sheet across the
sky that appears in many shapes.  It may be like unconnected piles or a layer of clouds
piled together.  A nimbostratus cloud is a smooth layer of
grey.

High clouds sometimes appear at height of more than
10,000 meters above the earth's surface. These clouds are formed entirely of ice
crystals. These clouds are further classified as cirrus, cirrostratus, and cirrocumulus
clouds. Cirrus clouds are the delicate wispy clouds that form high in the sky, sometimes
higher than 10,000 metres.  A cirrostratus cloud looks like a thin sheet.  Cirrocumulus
clouds look like many small tufts of cotton in the
sky.

Some clouds appear at more than on height. For
example, cumulus and cumulonimbus clouds may rise to great heights while their bases are
near the ground. A cumulonimbus cloud may reach heights as great as 18,000 metres from
its base so that its top consists of only ice crystals.