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I am using ERA5 data to drive the land surface model. One of the forcing required by LSM is specific humidity. We want to use the 2-m specific humidity. So how can I calculate the specific humidity based on dew point at 2 meters, surface pressure at 2 meters and temperature at 2 meters? I saw in ERA5 documentation we can calculate the 'saturated specific humidity' by some equations (https://confluence.ecmwf.int/display/CKB/ERA5%3A+data+documentation#ERA5:datadocumentation-Computationofnear-surfacehumidityandsnowcover). enter image description here But how can I get the specific humidity?

Thanks and hope for your early reply!

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The answer is easy. Replace $T$ with $T_d$, where $T_d$ is the dewpoint temperature.

I will say I am not all that familiar with those equations, but that is besides the point.

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Just in case it will save a great deal of time for others in the future, ill recommend the metpy package.

https://unidata.github.io/MetPy/latest/api/generated/metpy.calc.specific_humidity_from_dewpoint.html

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    $\begingroup$ Please expand the answer to detail the specifics of the package $\endgroup$
    – arkaia
    Jun 5 '21 at 12:20
  • $\begingroup$ The specifics are detailed in the link. In summary, it's a python function that requires the surface pressure and the dew point temperature and computes the specific humidity from these two variables. $\endgroup$
    – innomask
    Jun 5 '21 at 13:43
  • $\begingroup$ Yeah but the question is: is the equation shown in my question for saturated specific humidity? and if so, how can I calculate the specific humidity? (rather than saturated? $\endgroup$
    – Xu Shan
    Nov 16 '21 at 10:50

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