(GK) THE WORLD : Humidity

GK : THE WORLD

Humidity:
Humidity, the term used to express the dampness of the atmosphere, is due to the pressure of water vapour. Evaporation is the mean by which water is drawn off as invisible water vapour from oceans, lakes, rivers, etc., when the air contains as much water vapour as it can hold is said to be saturated. When saturated air is cooled, condensation takes place and some of the water which form the clouds grow larger, they precipitate i.e., fall to the earth as rain. The proportion of water vapour in the air, compared with the maximum it can hold at the same temperature, is known as Relative Humidity. Dew is caused by the condensation of water vapour on the cold ground during the night. 

The temperature at which such condensation takes place is called the Dew Point. When condensation takes place near the surface (and not on the ground) the result is usually mist or fog. When condensation takes place at some distance from the ground, clouds are formed. When water vapour is condensed at a temperature below freezing point it forms snow. There are various kinds of clouds. The layer like clouds often seen on the horizon at sunrise and sunset are called stratus clouds. The light wispy clouds formed high in the sky are called cirrus clouds. The heaped up clouds, looking rather like masses of cotton wool are called cumulus clouds. The black rain clouds are known as nimbus.

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