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Submitted By clarzmraz
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What is Humidity?? * Humidity is the state of atmosphere in relation to amount of water vapor it contains. Humidity is closely related to its temperature – higher the air temperature, more vapor the air can hold. * For this reason, saturation vapor pressure (ew) goes up with air temperature; i.e., as temperature goes up ew also goes up.
Significance of Humidity
The amount of water vapor in air effectively controls the weather condition by controlling evapotranspiration from land and water surfaces.
Evaporation rate is proportional to difference between saturated vapor pressure at water temperature (ew) and actual vapor pressure in air (ea).
EL = C (ew – ea),
Where, EL is lake evaporation rate, C is a constant of proportionality.
Causes of Humidity
Molecules of water having sufficient kinetic energy to overcome attractive forces tending to hold them within the body of liquid water are projected through the water surface into the air.
The process by which liquid water is converted into vapor is called vaporization or evaporation. Since the kinetic energy increases and surface tension decrease as temperature rises, evaporation rate increases with temperature.
Most of the atmospheric vapor is the product of evaporation from water surfaces. The direct transformation from ice to vapor, and vice versa, is called sublimation. The process by which vapor changes to the liquid or solid state is called condensation.
Properties of Water Vapor
The partial pressure exerted by water vapor is called vapor pressure (e). If all the water vapor in a closed container of moist air with an initial total pressure p were removed, then the final pressure p’ of dry air alone would be less than p.
Then, e = p – p’
When the maximum amount of water vapor for a given temperature is contained in a given space, the space is saturated with water vapor. The pressure exerted in a…...

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