[Wrf-users] How to get RH field from dew point using ungrib?

[Elisabeth Donnell]

Hello wrf-users, 

I am using CMC to drive WRF-NMM (V3.2). My input grib files contain dew point at 2m and dew point depression at other vertical levels (not RH). 

I think that WRF needs as input an RH field. I noticed there is some code in the ungrib (rrpr.F) that looks like it should do the conversion for me (see at end of email). 
My question is therefore ...is there something I should be doing to utilise this code, as at present when I run ungrib, RH does not appear in the intermediate file ? Should I set up my Vtable (and METGRID.TBL) differently? 

Any ideas much appreciated. 

This is the section of code I am referring to in in rrpr.F 
! If surface RH is missing, see if we can compute RH from Specific Humidity 
! or Dewpoint or Dewpoint depression: 
! 
if (.not. is_there (200100, 'RH')) then 
if (is_there(200100, 'TT').and. & 
is_there(200100, 'PSFC' ) .and. & 
is_there(200100, 'SPECHUMD')) then 
call get_dims(200100, 'TT') 
call compute_rh_spechumd(map%nx, map%ny) 
call mprintf(.true.,DEBUG, & 
"RRPR: SURFACE RH is computed") 
elseif (is_there(200100, 'TT' ).and. & 
is_there(200100, 'DEWPT')) then 
call get_dims(200100, 'TT') 
call compute_rh_dewpt(map%nx, map%ny) 
elseif (is_there(200100, 'TT').and. & 
is_there(200100, 'DEPR')) then 
call get_dims(200100, 'TT') 
call compute_rh_depr(map%nx, map%ny, 200100.) 
endif 
endif 

and the Vtable 
wrf at model11:/var/domains/AUS9_CMC/wpsprd$ more Vtable 
GRIB1| Level| From | To | metgrid | metgrid | metgrid | 
Param| Type |Level1|Level2| Name | Units | Description | 
-----+------+------+------+----------+---------+------------------------------------------+ 
11 | 100 | * | | TT | K | Temperature | 
33 | 100 | * | | UU | m s-1 | U | 
34 | 100 | * | | VV | m s-1 | V | 
7 | 100 | * | | HGT | m | Height | 
11 | 105 | 2 | | TT | K | Temperature at 2 m | 
17 | 105 | 2 | | DEWPT | K | Dew point temperature at 2 m | 
33 | 105 | 10 | | UU | m s-1 | U at 10 m | 
34 | 105 | 10 | | VV | m s-1 | V at 10 m | 
81 | 1 | 0 | | LANDSEA | proprtn | Land/Sea flag (1=land,0=sea) | 
2 | 102 | 0 | | PMSL | Pa | Sea-level Pressure | 
80 | 1 | 0 | | SST | K | Sea Surface Temperature | 
76 | 100 | * | | QC | kg kg-1 | Cloud water mixing ratio 
-----+------+------+------+----------+---------+------------------------------------------+ 


Cheers, 

Liz 


Dr. Elisabeth Donnell 

weatherzone° 
M 0425322032 
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