[Met_help] Re: MET package question -- water vapor

[Lacey Holland]

Hi, Brian!

Here's the answer on specific humidity.  You are correct, the units for 
prepbufr are mg/kg, while the grib is kg/kg.  We're adding in the 
conversion for the next release.  Thanks for the question!


--Lacey



Brian Gaudet wrote:
>
> Hi Lacey,
>
> No, thanks for forwarding this to met_help.  It is still possible that 
> I am
> doing something wrong of course, either with MET or with the WRF
> PostProcessor, but hopefully at met_help people will know the units
> they had in mind for these quantities and be able to quickly see
> if I am in fact goofing up.
>
>
> Brian
>
>
>
>
>
>
> On Wed, Nov 28, 2007 10:09 AM, *Lacey Holland <lholland at ucar.edu>* wrote:
>
>     Hi, Brian!
>
>     I'm cc'ing this to met_help, since I think it may be of interest to 
>     others around here.  I hope you don't mind.  ;)
>
>     You are right - if the units are different, then it wouldn't make sense 
>     to verify until you get them into the same units.  Right now, I don't 
>     see an easy way around it, but I'll check on ways around it and see if 
>     others around here can think of solutions.  It may be a conversion we 
>     have to build into MET in a future release.  Currently, we're planning 
>     on building in conversations for relative humidity, dewpoint temperature 
>     and other calculated quantities into the next release, but I'll see what 
>     can be done about specific humidity.
>
>
>     Thanks for the heads up!  We certainly appreciate knowing about this 
>     problem!
>     --Lacey
>
>
>
>     Brian Gaudet wrote:
>     >
>     >
>     > Hi Lacey,
>     >
>     >
>     > I have run into some issues with regard to creating statistics for 
>     > water vapor
>     > in the atmosphere (some of which may be WRF postprocessor
>     issues).
>     >
>     > Specifically:
>     >
>     > 1)  It appears that the only water-vapor related variables the WRF-
>     > postprocessor handles for the GRIB output format are specific
>     > humidity and relative humidity.  Since relative humidity involves
>     > temperature as well, that leads us to verify specific humidity
>     > (as is specified in the default Config files provided with MET).
>     >
>     > 2)  During the verification of specific humidity, however,
>     > I've noticed that the units of this parameter in the
>     > forecast field (i.e., ultimately from WRF via the
>     > postprocessor) appear to be in units of kg/kg
>     > (with a sample FBAR  value of 0.002 near the surface
>     > this time of year)
>     >
>     > but the units of the observational field (i.e., from PrepBufr
>     > via pb2nc) appear to be in units 10^6 times smaller
>     > (i.e., the corresponding sample OBAR value is 1918.4).
>     >
>     > Obviously, comparing quantities this many orders of magnitude
>     > apart does not produce meaningful statistics.
>     >
>     >
>     > The situation would be consistent with the observational-oriented
>     > code trying to convert g/kg observations into kg/kg but accidentally
>     > multiplying instead of dividing by 10^3.   But I have not yet
>     > been able to figure out how to modify the code in order to correct
>     > (or test) this.
>     >
>     >
>     > Do you know if I am doing anything wrong, or if not do you know
>     > how this problem may be corrected?
>     >
>     >
>     > Thanks,
>     >
>     > Brian Gaudet
>     >
>     >
>     >
>     >
>     >
>
>
>     -- 
>     ____________________________
>     Lacey Holland
>
>     UCAR/NCAR, Research Applications Laboratory
>     P.O. Box 3000
>     Boulder, CO  80307
>     (303) 497-8396
>
>
>
>         
>


-- 
____________________________
Lacey Holland

UCAR/NCAR, Research Applications Laboratory
P.O. Box 3000
Boulder, CO  80307
(303) 497-8396