How to calculate the specific humidity based on the saturated specific humidity?

Question

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).

But how can I get the specific humidity?

But how can I get the specific humidity?
Thanks and hope for your early reply!

BarocliniCplusplus · Answer

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.

innomask · Answer

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

How to calculate the specific humidity based on the saturated specific humidity?

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