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(RESOLVED) ERA-Interim data - using specific humidity instead of RH

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New member
I'm running WRF with ERA-Interim data(pressure level, RH not included), can I use specific humidity, 2m temperature and 2m dewpoint temperature to calculate relative humidity instead of ungribbing it from ERA-interim RH data file during the ungrib procedure?
I simply add SPECHUMD to the Vtable.ECMWF and others are the same.
Then I notice this RH data calculated from SPECHUMD, 2m TT and 2m DEWPT are different from the ungribbed ERA-Interim RH data in met_em*.nc, what could be the problem?

Thanks so much,
It's hard to say what the difference is, but if you have specific humidity available, you do not need to worry about having or calculating RH. That process will be done for you. See this section of the Users' Guide, regarding mandatory input data: