Re: [netcdf-java] [thredds] Help with GRIB encoding - what is "reference time of data" ??

  • To: Eizi TOYODA <toyoda@xxxxxxxxxxxxxx>
  • Subject: Re: [netcdf-java] [thredds] Help with GRIB encoding - what is "reference time of data" ??
  • From: John Caron <caron@xxxxxxxxxxxxxxxx>
  • Date: Tue, 26 Nov 2013 08:09:35 -0700
Hi Eizi:

Thanks for clarifying that terminology, I see that my understanding has been a bit fuzzy. I think I do indeed mean "Start of forecast", not the actual time the model was run.

Does your agency still use GRIB-1? If so, do you ever code anything other than the "Start of forecast" in the reference time ?

If you use GRIB-2, do you set "Significance of reference time" equal to 1 = "Start of forecast" ?

Finally, what in your opinion is the meaning of the other "Significance of reference time" codes, esp how does "Analysis" differ from "Start of forecast" ?


On 11/26/2013 2:23 AM, Eizi TOYODA wrote:
Hi John,

I'm not sure what do you mean by "run time".

If you want the date/time at which the forecast model started, I don't
think GRIB contains it.

If you mean the initial time of forecast model, that is "Start of
forecast" and it is really common to use this as reference time.

Eizi TOYODA: Japan Meteorological Agency
Associate member of WMO/CBS/OPAG-ISS/IPET-DRMM

Best Regards,
Eiji (aka Eizi) TOYODA

On Sat, Nov 23, 2013 at 3:03 AM, John Caron <caron@xxxxxxxxxxxxxxxx
<mailto:caron@xxxxxxxxxxxxxxxx>> wrote:

    The question is whether the CDM can assume that GRIB "Reference time
    of data" is the "run time" of a forecast model.

    In GRIB-1 docs, in the PDS there is:

    "Reference time of data – date and time of start of averaging or
    accumulation period"

    In GRIB-2 in Identification section, there is:

    12 Significance of reference time (see Code table 1.2)

    Reference time of data:

    13–14 Year (4 digits)
    15 Month
    16 Day
    17 Hour
    18 Minute
    19 Second

    And Code table 1.2 has the following:

    Code Table Code table 1.2 - Significance of reference time (1.2)
         0: Analysis
         1: Start of forecast
         2: Verifying time of forecast
         3: Observation time
        -1: Reserved
        -1: Reserved for local use
       255: Missing

    None of this obviously refers to "run time", although I suspect
    that's how many centers use it. However, it appears that when you
    want to define a time interval, say "average of the temperature,
    starting 12 hours and ending 24 hours from reference, you may use
    the reference time to define the start of that interval. In which
    case, its not the runtime. Im hoping thats not the case, that
    reference time is the same as the run time for forecast models.

    So if you know how to interpret these for any or all datasets,
    please send me a note, or post to this group. Please pass this
    question on to anyone who might be willing to contribute.



    thredds mailing list
    thredds@xxxxxxxxxxxxxxxx <mailto:thredds@xxxxxxxxxxxxxxxx>
    For list information or to unsubscribe,  visit:

  • 2013 messages navigation, sorted by:
    1. Thread
    2. Subject
    3. Author
    4. Date
    5. ↑ Table Of Contents
  • Search the netcdf-java archives: