[ncl-talk] Read correctely WAFS_blended GRIB2 file

Fri Aug 22 09:35:12 MDT 2014

I checked in a fix for this problem late yesterday, so it will be in the
new release.
 -dave

On Thu, Aug 21, 2014 at 5:59 PM, David Brown <dbrown at ucar.edu> wrote:

> NCL 6.2.1 is going to be released very soon. I am hoping that I will be
> able to get this fix into the code in time.
>  -dave
>
>
> On Thu, Aug 21, 2014 at 5:57 PM, Rabah Hachelaf <hachelaf at sca.uqam.ca>
> wrote:
>
>> Hi Dave and all,
>>
>> Thanks for your answers,
>> When do you plan the next NCL release, Dave ?
>>
>> Rabah
>>
>>
>> 2014-08-21 19:19 GMT-04:00 David Brown <dbrown at ucar.edu>:
>>
>> I have determined that there is indeed a bug in the NCL GRIB2 module. I
>>> am creating a ticket and expect to have a fix in time for the next release.
>>> (6.2.1) Sorry for the inconvenience.
>>>  -dave
>>>
>>>
>>> On Thu, Aug 21, 2014 at 1:57 PM, David Brown <dbrown at ucar.edu> wrote:
>>>
>>>> I am currently trying to figure out where wgrib2 finds the level
>>>> numbers. The NCEP g2clib (the low-level GRIB2 library that NCL relies on)
>>>> reports all the fields with multiple levels as having level type 255 (which
>>>> means undefined or missing), and the level values as 0. So I am trying to
>>>> go through the wgrib2 code to figure out where it is getting the various
>>>> level numbers (and the units of "mb").
>>>>  -dave
>>>>
>>>>
>>>> On Thu, Aug 21, 2014 at 1:30 PM, Dennis Shea <shea at ucar.edu> wrote:
>>>>
>>>>> wgrib2 -netcdf ....    works.  The generated nc file is 'technically
>>>>> correct'.   However, it is not the way most nc files are constructed.
>>>>>
>>>>> Going back a bit, GRIB is a record format *not* a file format like,
>>>>> say,
>>>>>  netCDF or HDF. Each GRIB record is for one level only.
>>>>> There are *no rules* for how a collection of GRIB records should be
>>>>> structured
>>>>> within a file.
>>>>>
>>>>> Hence, the GRIB records could be in random order and placed within one
>>>>> file.
>>>>> The great feature of NCL is that it reorders the GRIB records
>>>>> according to time and, if multiple level, collects the levels, etc. It does
>>>>> this 'on the fly'. The output looks like the variable came from a netCDF
>>>>> file.
>>>>>
>>>>>
>>>>> It looks like  'wgrib2 -netcdf ...' took each grib record and created
>>>>> a different variable for one time step.
>>>>>
>>>>>       float CTP_700mb ( time, latitude, longitude )
>>>>>          _FillValue :    9.999e+20
>>>>>          short_name :    CTP_700mb
>>>>>          long_name :    In-Cloud Turbulence
>>>>>          level :    700 mb
>>>>>          units :    percent
>>>>>
>>>>>       float CTP_600mb ( time, latitude, longitude )
>>>>>          _FillValue :    9.999e+20
>>>>>          short_name :    CTP_600mb
>>>>>          long_name :    In-Cloud Turbulence
>>>>>          level :    600 mb
>>>>>          units :    percent
>>>>>
>>>>> [snip]
>>>>>
>>>>> A common netCDF file might have
>>>>>
>>>>>      level = 5
>>>>>
>>>>>      float CTP (time, level, latitude, longitude)
>>>>>
>>>>>      level(level) ....
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Thu, Aug 21, 2014 at 12:35 PM, HAVENER, KEVIN F GS-12 USAF AFWA 14
>>>>> WS/WXED <kevin.havener at us.af.mil> wrote:
>>>>>
>>>>>> Rabah,
>>>>>>
>>>>>> I can't say with too much authority what is going on here, but I
>>>>>> think the grib2 file was created by concatenating a bunch of single-level
>>>>>> grib files together and ncl_filedump sees the two differently named fields
>>>>>> and the first two or so of identically named fields (that have some
>>>>>> different metadata) and that’s all.
>>>>>>
>>>>>> I found the same problem you did when you view the file with
>>>>>> ncl_filedump and not surprisingly ncl_convert2nc gave the same result.
>>>>>> However, I used wgrib2's -netcdf option to convert the file to netcdf and
>>>>>> got a netcdf file that looks much more like the original grib (gzip'ed
>>>>>> netcdf attached) and probably what you expected to see.
>>>>>>
>>>>>> I've attached the ncl_filedump of my converted file to this email and
>>>>>> will mail you a copy of the converted file (3 mb) directly to you rather
>>>>>> than the list.
>>>>>>
>>>>>> Kevin Havener
>>>>>>
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: ncl-talk-bounces at ucar.edu [mailto:ncl-talk-bounces at ucar.edu]
>>>>>> On Behalf Of Rabah Hachelaf
>>>>>> Sent: Thursday, August 21, 2014 1:34 PM
>>>>>> To: ncl-talk
>>>>>> Subject: [ncl-talk] Read correctely WAFS_blended GRIB2 file
>>>>>>
>>>>>>
>>>>>> Hi all,
>>>>>>
>>>>>> I am trying to plot icing, turbulence for several pressure levels
>>>>>> from WAFS_blended GRIB2 files, which can be find attached.
>>>>>>
>>>>>> The inventory of this file type is in this link:
>>>>>> http://www.nco.ncep.noaa.gov/pmb/products/gfs/WAFS_blended_2012010606f06.grib2.shtml
>>>>>>
>>>>>> When i use ncl_filedump i can't find any information about pressure
>>>>>> levels, it seems like there only one level although in the inventory file
>>>>>> there is several levels.
>>>>>>
>>>>>> Thanks to help me about this.
>>>>>>
>>>>>> Rabah
>>>>>> --
>>>>>>
>>>>>> ------------------------------
>>>>>> Cordialement,
>>>>>> Best regards,
>>>>>> Rabah Hachelaf
>>>>>>
>>>>>>
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>>>>>>
>>>>>>
>>>>>
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>>>>
>>>
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>>
>>
>> --
>> ------------------------------
>> Cordialement,
>> Best regards,
>> Rabah Hachelaf
>>
>
>
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