CLOUDS AND THEIR TYPES

CLOUDS AND THEIR TYPES

When air is cooled below its dew point temperature, the excess water vapor condenses into minute particles of water, which remain suspended in the air. Millions of such particles, close together, become visible as cloud.

The cooling of air below its dew point can be due to any of the 4 causes - 

• contact with cold surface of land or sea
• adiabatic cooling during ascent
• contact with colder masses of air 
• radiation of heat into space by upper layers of air

Clouds can form at any height from sea level up to the tropopause, which is about 8 km above the poles, about 13.5 km above temperate latitudes and about 16 km above the equator. 

They are hence grouped according to their height of base above sea level - 

• low clouds - having their bases between sea level and 2 km height.
• medium clouds - they have the prefix "alto" to their names and have bases between 2 km and 6 km above sea level.
• high clouds - they have the prefix "cirro" to their names and have bases between 6 km above sea level and the tropopause(i.e. about 8 km above poles and 16 km above the equator)

These heights are average only. 

The tops of medium clouds and the bases of high clouds can overlap by as much as 3 km.

Clouds are of four main types, classified according to their appearance:

• Cirrus - a silvery cloud in the form of feathers or fibres seen high up in a blue sky
• Cumulus - a white cloud, shaped like a cauliflower, which can have great vertical extent
• Stratus - an even layer of grey cloud, not giving rain
• Nimbostratus - An even layer of grey cloud giving rain.

Grouping of Clouds according to height

Given below is a brief description of the 10 clouds listed above - 

CIRRUS

1.Cirrus - Silvery, high clouds appearing like feathers or fibres. Being so high up, they always have a background of blue sky and, during twilight often appear bright red or yellow. 

CIRROSTRATUS

2.Cirrostratus - A thin white veil of high cloud through which the Sun or Moon have a watery look. 

CIRROCUMULUS

3.Cirrocumulus - A high layer of cloud in the form of small flakes or cauliflowers, white in colour with no dark shadows in between.

ALTROSTRATUS

4. Altostratus - A thin greyish or bluish veil of cloud through which the sun or moon appears very dim - as if seen through frosted glass.

ALTOCUMULUS

5. Altocumulus - Clouds in patch, layer or sheet form, white or grey or both in color. They have the appearance of small flattened globules or rolls or long bands or almonds, all of which may be in regular patterns aligned in one, or sometimes two, directions.

STRATUS

6.Stratus - A low even layer of dark grey cloud with light and dark patches.It has a dry look and does not cause precipitation. It can obscure the Sun completely and can greatly weaken daylight.

NIMBOSTRATUS

7. Nimbostratus - A low,even layer of dark-grey cloud generally uniform and threatening in appearance with no light coloured patches.It has a wet look and can also obscure the Sun completely like the Stratus clouds.

STRATOCUMULUS

8. Stratocumulus - Clouds consisting of a layer or patches of globular masses which appear soft. The patches often join together and form an overcast sky, but is distinguishable from stratus by its wavy or linear appearance.

CUMULUS

9. Cumulus - Brilliant white , thick clouds with flat bases and rounded cauliflower like tops.The outline of such cloud is very clear cut. Precipitation, if any, caused by even, well developed cumulus is light.

CUMULONIMBUS

10. Cumulonimbus - Mass of grey, heavy cloud having its base in low cloud level, of great vertical extent, with its top well in high cloud level. It has a threatening appearance and is called a thundercloud. Cumulonimbus gives intermittent precipitation with rapidly fluctuating intensity.

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