problem about relative humidity from GDAS

[Guangyao Dai]

Hi,
Recently I am trying to calibrate the water vapor mixing ratio (WVMR) from lidar by comparing it to the WVMR calculated from the GDAS data. But I have one question about the relative humidity from the GDAS. There is no doubt that I can calculate the WVMR using the temperature, press and relative humidity from GDAS when the temperature is greater than 0 ℃ (pure liquid water) and below -20℃ (pure ice).
However, if the temperature is between 0 and -20 ℃ (mixture of liqiud water and ice), what should I do to calculate the WVMR from the GDAS data? What's the fraction of the liquid water or the ice?
Thanks very much for taking care.
Guangyao Dai

[barbara.stunder]

Please give an example filename of the GDAS files you are using.

[Guangyao Dai]

Please give an example filename of the GDAS files you are using.

Hi, the filename of the GDAS file I am using is "pro_20150412_18_39_69.gdas1" .

The contents:
Used Nearest Grid Point ( 70, 130) to Lat: 39.00, Lon: 69.00
2D Fields
PRSS MSLP TPP6 UMOF VMOF SHTF DSWF RH2M U10M V10M T02M TCLD SHGT CAPE CINH LISD LIB4 PBLH TMPS CPP6 SOLM CSNO CICE CFZR CRAI LHTF LCLD MCLD HCLD WDIR WSPD
hPa hPa mm W/m2 W/m2 % m/s m/s oC % m m oC W/m2 % % % deg m/s
688 688 1019 0 0 0 0 48.0 75.0 -0.31 1.1 -8.3 92.0 3284 0 0 280 0 19.0 -14.0 0 0.47 0 0 0 0 0 0 1.0 92.0 164.8 1.2
3D Fields
HGTS TEMP UWND VWND WWND RELH TPOT WDIR WSPD
m oC m/s m/s mb/h % oK deg m/s
1000 207 23.3 0 1.6 29.1 42.8 296.5 180.0 1.6
975 422 21.8 0 1.6 29.1 42.8 297.1 180.0 1.6
950 641 20.6 0 1.6 29.1 42.8 298.1 180.0 1.6
925 866 19.1 0 1.6 29.1 42.8 298.8 180.0 1.6
900 1096 17.5 0 1.6 29.1 42.8 299.6 180.0 1.6
850 1573 14.4 0 1.6 29.1 42.8 301.3 180.0 1.6
800 2075 11.1 0 1.6 29.1 42.8 303.0 180.0 1.6
750 2606 7.7 0 1.6 29.1 42.8 305.0 180.0 1.6
700 3168 4.0 0 1.6 29.1 42.8 306.9 180.0 1.6
650 3767 0.92 0 3.3 24.4 30.0 310.0 180.0 3.3
600 4406 -2.0 1.2 2.9 28.7 9.0 313.8 202.3 3.2
550 5092 -6.1 3.1 1.7 28.6 8.0 316.9 241.2 3.6
500 5830 -11.2 7.3 1.0 17.8 20.0 319.4 261.8 7.3
450 6629 -17.1 10.6 0.45 2.6 52.0 321.7 267.6 10.6
400 7501 -23.6 14.6 -3.5 -3.8 95.0 324.4 283.6 15.0
350 8464 -30.4 18.0 -9.7 -9.4 93.0 327.8 298.3 20.4
300 9541 -39.1 17.1 -11.0 -5.0 69.0 330.3 302.9 20.4
250 10760 -50.3 14.3 -11.0 4.8 87.5 331.3 307.7 18.0
200 12176 -61.2 16.7 -15.8 5.3 81.2 335.8 313.5 23.0
150 13950 -61.9 29.3 -14.3 1.7 20.4 363.5 296.0 32.6
100 16454 -64.3 14.4 -1.6 -0.24 5.3 403.5 276.2 14.5
50 20642 -63.2 6.0 2.4 494.7 248.6 6.5
20 26419 -48.8 5.3 4.2 686.9 231.5 6.8
Thanks for your help.
Guangyao Dai

[barbara.stunder]

We don't have a file of that name, but from your listing it must be from our one-degree pressure-level files
(ftp://arlftp.arlhq.noaa.gov/archives/gdas1/), which come from NOAA/NCEP's output files named in this format: gdas1.t00z.pgrb2.1p00.f000

NCEP runs the model and calculates/outputs the relative humidity. We take their values and re-pack them in the format for HYSPLIT. This question needs to be directed to NCEP because we don't know the details of the fraction of liquid water to ice at the temperature range 0 to -20 deg C.

You can contact http://www.ncep.noaa.gov/mail_liaison/.