Hi Muhammad,

By using this command you can obtain humidity_mixing ratiio(Water vapor mixing ratio)

 ./icbc2netcdf --grads -v,qv -t 1990120100 -e 19910100 regcm.in
float qv(time, kz, iy, jx) ;
        qv:standard_name = "humidity_mixing_ratio" ;
        qv:long_name = "Water vapor mixing ratio" ;
        qv:coordinates = "xlon xlat" ;
        qv:units = "kg kg-1" ;


By using this command you can obtain relative humidity from ATM files
./rcm2netcdf --grads -a -v,rh -t 199012 -e 199102 regcm.in 


The blue ones are fixed, you can change other parts according to your date


I checked it with netcdf also  and 

 float rh(time, kz, iy, jx) ;
        rh:standard_name = "relative_humidity" ;
        rh:long_name = "Relative Humidity" ;
        rh:coordinates = "xlon xlat" ;
        rh:units = "1" ;
it seems that the netcdf and ctl files contain relative humidity data set.

Best Wishes