[Met_help] MET/pcp_combine help

Wed Feb 3 11:24:06 MST 2010

Jeff,

Very good question.  And I think the answer is that pcp_combine can't currently do that.  The "subtract" option for pcp_combine only allows you to specify the HH of the accumulation interval, not
HHMMSS.  So you'd only be able to perform the subtraction at the top of each hour.

Enhancing pcp_combine to allow you to specify HHHMMSS would be pretty straight-forward, but there would be implications for other MET tools.  Right now, pcp_combine creates a NetCDF file where the
variables for precip are named as "APCP_HH" where HH indicates the accumulation interval.  If we allow off-hour forecasts to be used, we'd need to generalize the variable names from "APCP_HH" to
"APCP_HHMMSS".  So we'd need to enhance the other MET tools to read that data.

Is this a pressing need for you?  Do you need to combine off-hour data in this way for your verification?  I'm also curious about your observations.  Do you really have observed precip that's
accumulated to 15 minutes after the hour?

If this is an issue that's standing in your way of using MET, we could probably figure out a fix.  We could enhance the code to allow you to specify HHMMSS for pcp_combine.  If you do need to pursue
this, please send me some sample data that includes some off-hour accumulations and a description of the pcp_combine function you'd like to perform.

Thanks,
John

Jeffrey Duda wrote:
> John,
> I have one more question for you.  If I wanted to use pcp_combine to get
> hourly precipitation from run total accumulated precip from WRFPRS files
> that are off-hour (like WRFPRS_d02.008_15), how would I indicate that when
> typing in the subtract args in the pcp_combine -subtract command?
> 
> Jeff Duda
> 
> On Sun, Jan 3, 2010 at 8:46 PM, John Halley Gotway <johnhg at rap.ucar.edu>wrote:
> 
>> Jeff,
>>
>> Sorry for the delay in getting back to you.
>>
>> Actually, the output of the PCP-Combine tool is a NetCDF file.  We use
>> NetCDF as our internal file format.  The other MET tools, like Grid-Stat,
>> Point-Stat, MODE, and Wavelet-Stat are all able to read GRIB files or the
>> NetCDF output of the PCP-Combine tool.
>>
>> For the next release of MET, we're working on generalizing our support for
>> NetCDF so that we're able to read more flavors of NetCDF and not just the
>> output of the PCP-Combine tool.
>>
>> Since the output is NetCDF, I'd suggest using the ncdump or ncview tools
>> to display/interrogate the data.  And let me refer to the MET User's Guide
>> (
>> http://www.dtcenter.org/met/users/docs/users_guide/MET_Users_Guide_v2.0_rev2.pdf
>> )
>> for more details.
>>
>> Hope that helps.
>>
>> John
>>
>>> John,
>>> I was able to successfully run copygb with your help and now am looking
>> to
>>> run pcp_combine, subtract, to get a one hour precip field from my WRF
>>> output
>>> files.  I have isolated the two files (and actually uploaded them to the
>>> server described in previous emails), and used the following command to
>>> run
>>> pcp_combine assuming the following:
>>>
>>>   "accum1" indicates the accumulation interval to be used from in_file1
>> in
>>> HH format (required).   -I set this as 12
>>>   "accum2" indicates the accumulation interval to be used from in_file2
>> in
>>> HH format (required).   -I set this as 11
>>>
>>> I got this:
>>>
>>> /bin/pcp_combine -subtract WRFPRS_d02.012_00 12 WRFPRS_d02.011_00 11
>>> difference.out
>>> Reading input file: WRFPRS_d02.012_00
>>> Reading input file: WRFPRS_d02.011_00
>>> Performing subtraction command.
>>> Writing output file: difference.out
>>>
>>> Figuring that pcp_combine took the difference between two GRIB files, the
>>> output should also be grip, no?  So I tried to convert it to view using
>>> Grads, but got an error when I ran grib2ctl.pl:
>>> "/grib2ctl.pl difference.out > difference_ctl.ctl
>>> found unidentified data
>>> Big problem:
>>>   either difference.out is missing or not a grib file
>>>   or wgrib is not on your path
>>>
>>> Please help.  Thank you very much for your help so far.
>>>
>>> Jeff Duda
>>>
>>> On Fri, Dec 18, 2009 at 3:45 PM, John Halley Gotway
>>> <johnhg at rap.ucar.edu>wrote:
>>>
>>>> Jeff,
>>>>
>>>> Well I'd first check to see what's actually in that GRIB file using the
>>>> "wgrib" command.  For example, try this:
>>>> wgrib WRFPRS_d02.012_00 | grep APCP
>>>>
>>>> That'll dump out the contents of that GRIB file, looking only for the
>>>> APCP
>>>> records (accumulated precip).  Look to see if that file really does
>>>> contain a record for 0-12 hour accumulated precip.
>>>>
>>>> If you have more questions about this, it'd probably be easier for you
>>>> to
>>>> just send me some sample data to take a look at.  If you'd like to do
>>>> that, you could post it to our anonymous ftp site in the following way:
>>>>
>>>> cd "the directory that contains the files you want to send"
>>>> ftp ftp.rap.ucar.edu
>>>> username = anonymous
>>>> password = "your email address"
>>>> cd incoming/irap/met_help
>>>> mkdir duda_data
>>>> cd duda_data
>>>> put WRFPRS_d02.012_00
>>>> put WRFPRS_d02.011_00
>>>> bye
>>>>
>>>> Hope that helps.
>>>>
>>>> John
>>>>
>>>>> John,
>>>>> I am Bill Gallus' student and I am trying to use MODE to verify a WRF
>>>>> model
>>>>> run using accumulated precip.  To do this, I need to match Stage_IV
>>>> data
>>>>> to
>>>>> my model grid.  To do that, though, I need to get a difference in
>>>> precip
>>>>> file to compare with Stage_IV data (which has 1 hourly accumulated
>>>>> precip).
>>>>> My WRF files use run total accumulated precip.  I have run WPP on the
>>>>> NetCDF
>>>>> output of the WRF files and now am trying to use pcp_combine -subtract
>>>> to
>>>>> basically subtract the total accumulated precip from one file from one
>>>> an
>>>>> hour before it (my NetCDF output interval is 15 minutes).  When I
>>>> tried
>>>> to
>>>>> run pcp_combine, though, I got an error.  Can you help me with this,
>>>>> please?  Thank you.
>>>>>
>>>>>
>>>>> Here's a screen grab of the command and error:
>>>>>
>>>>> -bash-3.2$ /usr/local/METv2.0/bin/pcp_combine -subtract
>>>> WRFPRS_d02.012_00
>>>>> 12
>>>>> WRFPRS_d02.011_00 11 20080719_18-17_precipdiff
>>>>> Reading input file: WRFPRS_d02.012_00
>>>>>
>>>>>
>>>>> ERROR: get_field() -> can't find grib code 61 with accumulation of 12
>>>>> hours
>>>>> in grib file: WRFPRS_d02.012_00
>>>>>
>>>>> Jeff Duda
>>>>> --
>>>>> Jeff Duda
>>>>> Iowa State University
>>>>> Meteorology Graduate Student
>>>>> 3134 Agronomy Hall
>>>>> www.meteor.iastate.edu/~jdduda<http://www.meteor.iastate.edu/%7Ejdduda>
>>>> <http://www.meteor.iastate.edu/%7Ejdduda>
>>>>
>>>>
>>>
>>> --
>>> Jeff Duda
>>> Iowa State University
>>> Meteorology Graduate Student
>>> 3134 Agronomy Hall
>>> www.meteor.iastate.edu/~jdduda <http://www.meteor.iastate.edu/%7Ejdduda>
>>> _______________________________________________
>>> Met_help mailing list
>>> Met_help at mailman.ucar.edu
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>>>
>>
>>
> 
> 