[Met_help] [rt.rap.ucar.edu #81625] History for question on pcp_combine -subtract

[John Halley Gotway via RT]

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  Initial Request
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Dear MET Help,

It appears that pcp_combine in MET v6.0 can subtract 2 GRIB files and automatically deduce the APCP grid from the model GRIB file, but I haven't seen a specific example.

If I'm correct in this assumption, would this example usage work:
pcp_combine -subtract WRF_f03.grb2 03 WRF_f02.grb2 02 OUTPUT_1h-DIFF_onModelGrid.nc

?

OR, do I need to parse out the APCP grids from the GRIB2 files (using wgrib2 utility) prior to running them through pcp_combine?

Thanks for the confirmation,
Jon

*****************************************************************
Jonathan Case;  Research Meteorologist at ENSCO, Inc./NASA
Short-term Prediction Research and Transition (SPoRT) Center
320 Sparkman Dr., Room 3000B; Huntsville, AL 35805
Emails: Jonathan.Case-1 at nasa.gov<mailto:Jonathan.Case-1 at nasa.gov> (preferred) or case.jonathan at ensco.com<mailto:case.jonathan at ensco.com>
Voice: 256.961.7504  ;  Fax: 256.961.7788
http://weather.msfc.nasa.gov/sport/
*****************************************************************



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  Complete Ticket History
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Subject: question on pcp_combine -subtract
From: John Halley Gotway
Time: Tue Aug 15 15:51:46 2017

Jon,

Yes, pcp_combine will search for APCP GRIB records with the requested
accumulation interval.  There is no need to parse out the APCP records
ahead of time.  Please try running your example with a higher
verbosity
level (i.e. like -v 4 or -v 5).  That'll tell you which record numbers
it's
reading and you can cross-check those by looking at the output from
wgrib2.

FYI, in case you've never done this, pcp_combine can also be used to
process fields other than precip.  For example:

pcp_combine -subtract \
    WRF_f03.grb2 'name="TMP"; level="P500";' \
    WRF_f02.grb2 'name="TMP"; level="P500";' \
    OUTPUT_TMP_P500_1h-DIFF_onModelGrid.nc

In this example, I replaced the "03" and "02" with a configuration
string
(i.e. like a mini config file).  Instead of looking for APCP records
with
that accumulation interval, it searches for the field/level you
requested.
So this example will compute the difference between the 3 and 2-hour
500mb
temperature fields.  Not sure you'd actually want to do this, but
having
the flexibility to process fields other than APCP has been quite
useful.

Thanks,
John

On Tue, Aug 15, 2017 at 2:19 PM, Case, Jonathan[ENSCO INC] via RT <
met_help at ucar.edu> wrote:

>
> Tue Aug 15 14:19:05 2017: Request 81625 was acted upon.
> Transaction: Ticket created by jonathan.case-1 at nasa.gov
>        Queue: met_help
>      Subject: question on pcp_combine -subtract
>        Owner: Nobody
>   Requestors: jonathan.case-1 at nasa.gov
>       Status: new
>  Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=81625 >
>
>
> Dear MET Help,
>
> It appears that pcp_combine in MET v6.0 can subtract 2 GRIB files
and
> automatically deduce the APCP grid from the model GRIB file, but I
haven't
> seen a specific example.
>
> If I'm correct in this assumption, would this example usage work:
> pcp_combine -subtract WRF_f03.grb2 03 WRF_f02.grb2 02
> OUTPUT_1h-DIFF_onModelGrid.nc
>
> ?
>
> OR, do I need to parse out the APCP grids from the GRIB2 files
(using
> wgrib2 utility) prior to running them through pcp_combine?
>
> Thanks for the confirmation,
> Jon
>
> *****************************************************************
> Jonathan Case;  Research Meteorologist at ENSCO, Inc./NASA
> Short-term Prediction Research and Transition (SPoRT) Center
> 320 Sparkman Dr., Room 3000B; Huntsville, AL 35805
> Emails: Jonathan.Case-1 at nasa.gov<mailto:Jonathan.Case-1 at nasa.gov>
> (preferred) or
case.jonathan at ensco.com<mailto:case.jonathan at ensco.com>
> Voice: 256.961.7504  ;  Fax: 256.961.7788
> http://weather.msfc.nasa.gov/sport/
> *****************************************************************
>
>
>

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