I am using NCEP_DOE reanalysis 2 data set. It include only relative humidity while I need specific humidity. How do I convert the relative humidity into specific humidity?


marked as duplicate by David LeBauer, arkaia, Fred, Peter Jansson, EnergyNumbers Jul 3 '15 at 22:37

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The Engineering Toolbox gives the following equation for converting relative humidity to specific humidity.

If we know the relative humidity of the moist air and the water vapor density and density of the air, the specific humidity can be expressed as:

x = 0.622 φ ρws / (ρ - ρws) 100%         (1)


x = specific humidity of air vapor mixture (kg/kg)

φ = relative humidity (%)

ρws = density of water vapor (kg/m3)

ρ = density of the moist or humid air (kg/m3)

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