![]() ![]() Now to make the air saturated (100 % relative humidity), So, relative humidity is expressed as % whereas absolute humidity is expressed in absolute terms. Now the relative humidity = 40 % => 0.2 kg of water vapor per 1 m 3 of air => the air can still hold 0.3 kg of water vapor since saturation occurs at 0.5 kg. That is, relative humidity will be 100% if 1 m 3 of air contains 0.5 kg of water vapor at temperature T (saturation temperature or saturation point).Īssume that 1 m 3 of air at a given time consists of 0.2 kg of water vapor at a temperature ‘T’. Let us assume that saturation occurs when 0.5 kg of water vapor is present in 1 m 3 of air. By changing temperature of air (by changing the saturation point): a decrease in temperature (hence, decrease in moisture-holding capacity/decrease in saturation point) will cause an increase in relative humidity and vice versa.Ĭonsider 1 m 3 of air at a temperature ‘T’.By adding moisture through evaporation (by increasing absolute humidity): if moisture is added by evaporation, the relative humidity will increase and vice versa.Relative humidity can be changed in either of the two ways. If the air has half the amount of moisture that it can carry, then it is unsaturated and its relative humidity is only 50%.Thus, relative humidity of the saturated air is 100%. At this temperature, the air cannot hold any additional amount of moisture. Air containing moisture to its full capacity at a given temperature is said to be ‘saturated’.The relative humidity determines the amount and rate of evaporation and hence it is an important climatic factor.Relative humidity is greater over the oceans and least over the continents (absolute humidity is greater over oceans because of greater availability of water for evaporation).With the change of air temperature, the capacity to retain moisture increases or decreases and the relative humidity is also affected. ![]() The percentage of moisture present in the atmosphere as compared to its full capacity at a given temperature is known as the relative humidity.The ability of the air to hold water vapour depends entirely on its temperature (Warm air can hold more moisture than cold air).The absolute humidity differs from place to place on the surface of the earth.It is the weight of water vapour per unit volume of air and is expressed in terms of grams per cubic metre.The actual amount of the water vapour present in the atmosphere is known as the absolute humidity.Water vapour present in the air is known as Humidity.The land maximum occurs in equatorial region because of high insolation and luxuriant.The highest annual evaporation occur in the sub-tropics of the western North Atlantic and North Pacific because of the influence of the Gulf Stream and the Kurishino Current, and in the trade wind zone of the southern oceans.The oceans contribute 84% of the annual total and the continents 16%. Evapotranspiration may be taken as the starting point in the hydrological cycle.The oceans covering 71% of the earth’s surface hold 97% of all the earth’s water reserves.The atmospheric moisture affects the human body’s rate of cooling by influencing the sensible temperature.The amount of water vapour present decides the quantity of latent energy stored up in the atmosphere for development of storms and cyclones.It thus plays a crucial role in the earth’s heat budget. Water vapour absorbs radiation- both incoming and terrestrial.Amount of water vapour (Humidity) is measured by, an instrument called Hygrometer. Water vapour in air varies from zero to four per cent by volume of the atmosphere (averaging around 2% in the atmosphere).The hydrological cycle maintains this balance. Since the total amount of moisture in the entire system remains constant, a balance is required between evapotranspiration and precipitation.When saturation is reached, clouds give away water in the form of precipitation.Evaporated water undergoes condensation and forms clouds.The moisture in the atmosphere is derived from water bodies through evaporation and from plants through transpiration (evapotranspiration).There is a continuous exchange of water between the atmosphere, the oceans and the continents through the processes of evaporation, transpiration, condensation and precipitation. ![]() Understanding these concepts is important to understand Forms of Condensation and Precipitation which will be discussed in future posts. ![]()
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