Re: 20040625: GRIB problem in decoders-3.0.2 - bug?

On Fri, 25 Jun 2004, Unidata Support wrote:

> >To: address@hidden
> >From: Arild Burud <address@hidden>
> >Subject: GRIB problem in decoders-3.0.2 - bug?
> >Organization: UCAR/Unidata
> >Keywords: 200406251028.i5PASJWb020515
>
> Hi,
> I recently installed decoders-3.0.2 on a new linux workstation, and
> found a problem... It seems like the update described as "added
> forecasttime variable to gribtocdl" may be involved in this.
> I try to convert a grib file that contains "monthly mean" of a
> parameter, this is stored according to the "grib standard" with flags
> indicating this in the grib section one: Octet 21 = 123 (="average"),
> octet 20 = 24 (="24 hour periods").

Hiya Arild,

Thanks again for the gribtocdl code. I wonder if version 3.0.0 had the
same problem as 3.0.2?  At first thought, I don't see how the
forecasttime variable could cause this problem but maybe there is a
dependancy that I over looked. I'll check it out.


Robb...
> When I use gribtocdl and gribtonc I end up with a netCDF file that
> contains two days of data, the first day contains only undefined values,
> the second contains the data from the grib file. See extracts from
> gribdump and ncdump below:
>
> -----------------------------------------------------
>                       Header : 1
>           Originating Center : 98 (European Center for Medium-Range
> Weather Forecasts - Reading)
>                      Process : 122 (ECMWF model 122)
>                         Grid : 255
>               points in grid : 29040
>                    Parameter : 34 (v)
>                        Units : m/s
>                   Level Type : Surface
>               Reference Time : 2004/04/01:12:00
>                    Time Unit : Hour
>         Time Range Indicator : Special average Algorithm 3
>                  Time 1 (P1) : 0
>                  Time 2 (P2) : 24
>         Decimal Scale Factor : 0
>          Binary Scale Factor : -10
>              Reference Value : 270.895752
>                Minimum Value : 270.8958
>               Number of Bits : 16
>                 BMS Included : TRUE
>                 GDS Included : TRUE
>          IsInternationalGrid : FALSE
>                 GRIB Edition : 1
>          Parameter Table Ver : 128
>      GDS representation type : 0 (Latitude/Longitude)
>            Number of columns : 240
>               Number of rows : 121
>             Number of points : 29040
>                 Kind of grid : rectangular
>            GDS res/comp flag : 0x80
>           GDS scan mode flag : 0
>      GDS no. of vert. coords : 0
>                       GDS Ni : 240
>                       GDS Nj : 121
>                      GDS La1 : 90.000000
>                      GDS Lo1 : -178.500000
>                      GDS La2 : -90.000000
>                      GDS Lo2 : 180.000000
>                       GDS Di : 1.500000
>                       GDS Dj : 1.500000
>                   grid values:
> Row 0:
>       271.4602 271.4602 271.4602 271.4602 271.4602 271.4602 271.4602
> <snip>
>
> ------------------------------------------------------
>
> <snip>
> // global attributes:
>               :record = "reftime, valtime" ;
>               :history = "2004-06-25 09:38:49 - created by gribtocdl" ;
>               :title = "Enter model definition here" ;
>               :Conventions = "NUWG" ;
>               :GRIB_reference = "Office Note 388 GRIB" ;
>               :GRIB_URL = "http://www.nco.ncep.noaa.gov/pmb/docs/on388/"; ;
>               :version = 0. ;
> data:
>
>   reftime = 107388, 107388 ;
>
>   valtime = 107412, 107388 ;
>
>   datetime =
>    "2004-04-01 12:00:00Z",
>    "2004-04-01 12:00:00Z" ;
>
>   valtime_offset = 24 ;
>
>   forecasttime =
>    "2004-04-02 12:00:00Z",
>    "" ;
>
> <snip>
> -----------------------------------------------------------
>
> If I modify the gribfile so that the "Time 2 (P2)" is reset to zero, the
> netCDF file comes out as expected, with only one date of data.
>
> Seems likely that this problem is connected to the "valtime_offset"
> calculation...
>
> I you need the unmodified grib file used in this example, it is
> available from http://noserc.met.no/34m20040400t1200.grib
>
>
> Yours,
> Arild Burud
> --
> ---------------------------------------------------------------------
> address@hidden       System Developer          Tel.: +47 22963035
> http://www.met.no                                  Fax.: +47 22963050
> Norwegian Service Centre for Climate Modelling,  http://noserc.met.no
> Norwegian Meteorological Institute,    PB 43 Blindern,    N-0313 Oslo
> ---------------------------------------------------------------------
>
>
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===============================================================================
Robb Kambic                                Unidata Program Center
Software Engineer III                      Univ. Corp for Atmospheric Research
address@hidden             WWW: http://www.unidata.ucar.edu/
===============================================================================