relative humidity

[ensiyeh]

Hi

I have a problem with WRF-ARW. I don't have relative humidity in WRF output. Could you help me on how to calculate relative humidity, please?
Thank you

 

[Ming Chen]

The Relative Humidity (RH) is simply the mixing ratio divided by the saturation mixing ratio. wrfout files include mixing ratio and T, from which you can easily obtain RH.

 

[ensiyeh]

Hi Ming

Thank you. I searched for the equation of relative humidity a lot. But I didn't find any equation to calculate relative humidity. Every equation needs something that I don't have in my WRF output. Could you write the equation, please?
Thank you

 

[Ming Chen]

Here is a small piece of Fortran to calculate relative humidity from mixing ratio:
real, parameter :: svp1=611.2
real, parameter :: svp2=17.67
real, parameter :: svp3=29.65
real, parameter :: svpt0=273.15
real, parameter :: eps = 0.622
rh = 1.E2 * (p*q/(q*(1.-eps) + eps))/(svp1*exp(svp2*(t-svpt0)/(T-svp3)))
Note that t (temperature), p (pressure) and q (mixing ratio) are output variables in wrfout.

 

[ensiyeh]

Hi Ming,

Thank you for your reply. At this formula, is t equal T2 and q equal Q2 in wrfoutput file? What about P? Which P in wrfoutput file will use for calculation? Could you guide me, please?
Thank you

 

[Ming Chen]

T is temperature, Q is water vapor mixing ratio, P is pressure.They are are available in wrfoiut files.