Thank you very much for your answers. At first I thought this was very
different from grib1 -- but now I think not-so-much. GRIB1 had center,
subcenter, process, and ParameterTableVersionNumber, all of which got
used (sometimes) to identify the table (and the table could get
overriddened anyway by a local copy), and it looks like identifying the
local table in GRIB2 could very well be a similar process. GRIB2 has
the advantage that at least all the WMO standard codes come from WMO
tables instead of being copies into the local tables.
On Fri, Nov 29, 2013 at 5:38 AM, TOYODA Eizi <toyoda.eizi@xxxxxxxxx
<mailto:toyoda.eizi@xxxxxxxxx>> wrote:
__
Hi Benno,
1) I had similar question before. I'm sorry I can't remember the
conclusion for GRIB, but for BUFR, there are several element
descriptors whose definition changed over time. WMO is trying to
maintain upper compatibility, but sometimes something happened
unfortunately. I guess it is safer to assume GRIB is in similar status.
2) Again I'm sorry the table posted at following site is the only
one maintained.
http://www.wmo.int/pages/prog/www/WMOCodes/WMO306_vI2/LatestVERSION/LatestVERSION.html
Collecting local tables is I think the next step.
3) You'll need the code of the originating centre (and probably
sub-centre) to identify the local table. By the way I think NCEP
and ECMWF are using different short names for GRIB parameters. So I
don't think it is easy for WMO to establish its standard name.
Sorry about unconfortable answers....
Eizi
----- Original Message -----
*From:* Benno Blumenthal <mailto:benno@xxxxxxxxxxxxxxxx>
*To:* TOYODA Eizi <mailto:toyoda@xxxxxxxxxxxxxx>
*Cc:* John Caron <mailto:caron@xxxxxxxxxxxxxxxx> ; THREDDS
community <mailto:thredds@xxxxxxxxxxxxxxxx> ; Java NetCDF
<mailto:netcdf-java@xxxxxxxxxxxxxxxx>
*Sent:* Thursday, November 28, 2013 2:33 AM
*Subject:* Re: [thredds] Help with GRIB encoding - what is
"reference time of data" ??
I have been looking at grib2, and was hoping I could get some
help on some lower-level metadata questions.
1) wmo code tables have version numbers which are also in the
data records -- is it sufficient to use a code table that has
version number greater than or equal to the number in the
record, or do we have to match the version number in the record?
WMO is on version 12, my test data of interest is version 1, I
would much rather have a single latest-and-greatest that keep
all twelve-and-counting versions.
2) there are xml versions of the wmo code tables, which can be
converted into something more programmatically useful. Is there
a standard set of converted tables, i.e. XML with clean
discipline, category, version coding? Can the same be said of
local tables, e.g. NCEP for starters?
3) my understanding so far is that to identify a scientific
parameter (a.k.a standard_name) in grib we need wmo table
version or local table version, data source (if local table),
discipline, category, parameter number, and where (and if) we
find this info depends on the PDS template number.
NCEP maps this to short names, though WMO does not. And you are
presumably mapping this to standard_names as well. Are these
mappings available, i.e. in XML format?
On Wed, Nov 27, 2013 at 5:05 AM, TOYODA Eizi
<toyoda@xxxxxxxxxxxxxx <mailto:toyoda@xxxxxxxxxxxxxx>> wrote:
Hi John,
Yes JMA still issues GRIB edition 1 for:
- bulletins sent to GTS since long time ago, and
- the reanalysis project JRA-25 and JRA-55 (coming).
In the reanalysis there are some products like monthly
average, for which
multiple model runs are used in a single message. In that
case my
understanding is that the reference time is set to the
beginning of the time
range.
Situations are similar in GRIB2. I'm hoping the ECMWF
reanalysis will start
using GRIB2 sometime. I'm afraid I don't know actual data
using "Verifying
time of forecast" (CT1.2:2).
The reason why GRIB distinguishes "Analysis" time (CT1.2:0)
and "Start of
forecast" (CT1.2:1) might be rather historic nowadays. It
has a root in the
difference between data, i.e. analysis and initialized
analysis (sometimes
called data for ft=0).
Analysis is a best estimate of the state of the atmosphere,
made from
observation and past numerical forecast. In the past NWP
centers used
methods called nudging or optimal interpolation (the latter
is same as what
geographers call kriging). The bad thing is the result may
contain
inbalance between wind and pressure, which causes unnatural
gravity wave in
the forecast. So people had to remove such inbalance after
analysis. That
is the "initialization" heavily mentioned in GRIB edition 1.
Recent NWP systems use variational assimilation, which has
less such
problem. So the analysis simply becomes the initial field
without much
changes. I don't think somebody still issues "initialized
analysis"
separated from "(uninitialized) analysis". In GRIB edition
2, the concept
remains in a footnote in the Code table 1.4, but usually the
analysis and
forecast are put in a single GRIB message for Forecast
products (CT1.4:1).
In short, people no longer cares.
Best,
Eizi
----- Original Message ----- From: "John Caron"
<caron@xxxxxxxxxxxxxxxx <mailto:caron@xxxxxxxxxxxxxxxx>>
To: "Eizi TOYODA" <toyoda@xxxxxxxxxxxxxx
<mailto:toyoda@xxxxxxxxxxxxxx>>
Cc: "THREDDS community" <thredds@xxxxxxxxxxxxxxxx
<mailto:thredds@xxxxxxxxxxxxxxxx>>; "Java NetCDF"
<netcdf-java@xxxxxxxxxxxxxxxx
<mailto:netcdf-java@xxxxxxxxxxxxxxxx>>
Sent: Wednesday, November 27, 2013 12:09 AM
Subject: Re: [thredds] Help with GRIB encoding - what is
"reference time of data" ??
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" ?
thanks,
John
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.
Best,
--
Eizi TOYODA: Japan Meteorological Agency
Associate member of WMO/CBS/OPAG-ISS/IPET-DRMM
Best Regards,
--
Eiji (aka Eizi) TOYODA
http://www.google.com/__profiles/toyoda.eizi
<http://www.google.com/profiles/toyoda.eizi>
On Sat, Nov 23, 2013 at 3:03 AM, John Caron
<caron@xxxxxxxxxxxxxxxx <mailto:caron@xxxxxxxxxxxxxxxx>
<mailto: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.
Thanks!
John
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--
Dr. M. Benno Blumenthal benno@xxxxxxxxxxxxxxxx
<mailto:benno@xxxxxxxxxxxxxxxx>
International Research Institute for climate and society
The Earth Institute at Columbia University
Lamont Campus, Palisades NY 10964-8000 (845) 680-4450
--
Dr. M. Benno Blumenthal benno@xxxxxxxxxxxxxxxx
<mailto:benno@xxxxxxxxxxxxxxxx>
International Research Institute for climate and society
The Earth Institute at Columbia University
Lamont Campus, Palisades NY 10964-8000 (845) 680-4450
