[ncl-talk] grib2 file read

Tue Jul 26 19:16:08 MDT 2016

Thanks David. Do I need to read the file as "binary" ?

Debasish

On Tue, Jul 26, 2016 at 6:12 PM, David Brown <dbrown at ucar.edu> wrote:

> I am afraid there have been some misunderstandings.
> First of all the file "ngac.t00z.aerf24.grib2" (actually called
> ngac.t00z.aerf24 on the ftp site if anyone else wants to download it)
> is
> not a GRIB file at all. A simple test if you suspect something is not GRIB:
>
> strings <filename> | grep GRIB
>
> If this produces nothing then it's definitely not a GRIB file (of
> course the presence of "GRIB" does not prove it is a GRIB file).
> To digress for a moment, if it is a GRIB file then the command,
>
> strings <filename> | egrep 'GRIB|7777'
>
> will produce alternating instances of 'GRIB' and '7777'. These strings
> mark the beginning and end of each GRIB record. This is true for both
> GRIB 1 and 2.
>
> strings ngac.t00z.aerf24 |grep GRIB
> produces nothing so it is not GRIB.
>
> Second, the warning messages that are emitted when an ngac file that
> is valid GRIB is read by NCL such as:
>
> warning: Entry (62006) not found in code table file
> /Users/shea/devel/lib/ncarg/grib2_codetables/ncep/4/4.3.table
>
> refer to entries not found in table 4.3 which is "type of generating
> process". This is not the same as table 4.233 "Aerosol Type"
> and so the number 62006 in this context has nothing to do with 62006
> ("Sulphate Dry") in the Aerosol Type table
>
> 62006 as a type of generating processing is not documented in the 4.3
> table and hence the message. Since type of generating process is
> usually of less concern to users I am considering eliminating the
> error message in this case.
>
> It is true that NCL does not yet make use of the 4.233 table. That is
> because it is an auxiliary table that needs to be used in the context
> of certain GRIB2 product templates that address aerosols. It does not
> contain actual parameters. Rather a parameter might be named, e.g.
> "Aerosol optical thickness" and based on the template there is another
> piece of metadata called "Aerosol Type" which is as documented in the
> "Aerosol Types" table. A small extension to our GRIB2 data model is
> required to handle these templates. We hope to implement it in time
> for 6.4.0 but that is not yet certain.
>  -dave
>
>
> On Tue, Jul 26, 2016 at 12:23 PM, Debasish Hazra
> <debasish.hazra5 at gmail.com> wrote:
> > Hi Dennis,
> >
> > The variables in the range  62000 to 62010 in the updated grib2 table
> > "http://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_table4-233.shtml" are
> > "optical depth" and has no units associated with them.
> >
> > 62000 Total Aerosol
> > 62001 Dust Dry
> > 62006 Sulphate Dry
> > 62008 Sea Salt Dry
> > 62009 Black Carbon Dry
> > 62010 Particulate Organic Matter Dry
> >
> > 62010-62016 are mixing ratios in kg/kg
> >
> > Debasish
> >
> >
> >
> > On Tue, Jul 26, 2016 at 2:13 PM, Dennis Shea <shea at ucar.edu> wrote:
> >>
> >> Again, I will forward this. please send to ncl-talk. Otherwise, I am
> just
> >> a middleman forwarding the emails.
> >>
> >> Usually the GRIB tables have units:
> >>
> >> Examples:
> >> http://www.ncl.ucar.edu/Document/Manuals/Ref_Manual/ncep_141.htm
> >> http://www.ncl.ucar.edu/Document/Manuals/Ref_Manual/ecmwf_132.htm
> >>
> >> NCL ... see GRIB section
> >> See:
> >>
> http://www.ncl.ucar.edu/Document/Manuals/Ref_Manual/NclFormatSupport.shtml
> >>
> >> On Tue, Jul 26, 2016 at 12:05 PM, Debasish Hazra
> >> <debasish.hazra5 at gmail.com> wrote:
> >>>
> >>> The link updated grib2 table is here :
> >>>
> >>> http://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_table4-233.shtml
> >>>
> >>> Thanks
> >>> Debasish
> >>>
> >>> On Tue, Jul 26, 2016 at 1:33 PM, Dennis Shea <shea at ucar.edu> wrote:
> >>>>
> >>>> The issue is that the NGAC grib tables are not publicly available.
> >>>> If you know of where they are located, they can be included within NCL
> >>>>
> >>>> In fact, there is a JIRA ticket on this:
> >>>>
> >>>> [JIRA] (NCL-2442) GRIB-2: warning: Entry (not found in code table file
> >>>> .../grib2_codetables/ncep/4/4.3.table
> >>>>
> >>>> Just yesterday, a comment was made on this ticket:
> >>>>
> >>>> ---------
> >>>>
> >>>> Unfortunately the "not found in code table file" errors
> >>>> that Dennis reported in this ticket cannot be corrected
> >>>> because the entries for that were not found are not documented
> >>>> by the NCEP GRIB2 web pages. Table 4.3 contains the generating process
> >>>> mapping. The values found in the file, all in the range 62000 to
> 62016,
> >>>> probably refer to local "generating processes" related to the NGAC
> >>>> model.
> >>>> If documentation can be found to describe these I would be happy to
> add
> >>>> them to the tables.
> >>>>
> >>>> The other option to get rid of these admittedly annoying
> >>>> messages might be to just not print the warnings for this piece of
> >>>> metadata
> >>>> since it is not usually of that much interest to the data consumer. I
> >>>> would
> >>>> be happy to consider this.
> >>>>
> >>>> ---------
> >>>> Note: the *values* returned by NCL are correct. The meta data is not
> >>>> because the
> >>>> NCEP GRIB2 web pages are not available.
> >>>>
> >>>> --------
> >>>>
> >>>> Again, if you know where the appropriate tables are located, please
> send
> >>>> to ncl-talk.
> >>>>
> >>>> THX
> >>>>
> >>>> On Tue, Jul 26, 2016 at 11:21 AM, Debasish Hazra
> >>>> <debasish.hazra5 at gmail.com> wrote:
> >>>>>
> >>>>> Hi,
> >>>>>
> >>>>> I am trying to read grib2 file with ncl (v6.3) and it shows the
> >>>>> following error while trying to open it:
> >>>>>
> >>>>> fatal:An internal error has occurred. The file format requested does
> >>>>> not appear to be supported, could not open (ngac.t00z.aerf24.grib2)
> >>>>> Variable: f
> >>>>> Type: file
> >>>>> (0) File Missing Value : -1
> >>>>>
> >>>>> I kept the data file in ftp. Any help on this is appreciated.
> >>>>>
> >>>>> Thanks.
> >>>>> Debasish
> >>>>>
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> >>>
> >>>
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