Earth Humidity refers to the amount of water vapour present in the air.
The ratio between the amount of water vapour actually present in the air mass and the maximum amount that the air mass can hold at that temperature is called relative humidity. It is expressed as a percentage. It varies inversely with temperature, given a fixed amount of water vapour.
Absolute humidity denotes the actual quantity of water vapour present in the air and it is defined as the weight of water vapour (grams) in a given volume of air (cubic meter).
The term specific humidity is applied to express the ratio of weight of water vapour to the weight of moist air (including water vapour). It is stated as grams of water vapour per kilogram of moist air.
Earth Humidity is measured by an instrument called hygrometer. Another instrument used for the same purpose is sling psychrometer.
Condensation, Dew Point and Related Aspects
The physical process of transformation from the vapour to the liquid state is condensation. This is the basis of all types of precipitation- the fall of water from the atmosphere to the ground in any form.
Dew point is the temperature at which the air is fully saturated and below which condensation normally occurs.
Dew is the deposition of water droplets on the ground. It occurs when the temperature of the ground surface falls and the air in contact with it is cooled below its dew point. Dew is likely to occur on clear and calm nights.
Frost is a weather condition that occurs when the air temperature is at or below 0°c moisture on the ground surface and objects freezes to form an icy deposit.
Fog is made of the droplets of water suspended in the lower layers of the atmosphere, resulting from the condensation of water vapour around nuclei of floating dust or smoke particles. A visibility of less than 1 km is the internationally recognized definition of fog. Fog is not considered as a form of precipitation.
Smog (Smoke + Fog) is a form of fog that occurs in areas where the air contains a large amount of smoke.
Mist is the term for reduction of visibility between 1-2 km, caused by condensation producing water droplets within the lower layers of atmosphere.
Haze is formed by water particles that have condensed in the atmosphere and the visibility in this case is more than 1 km but less than 2 km. Haze may also be produced by presence of dust and smoke, which reduce visibility.
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