In progress. All details still to be updated..

General requirements

Encoding format

  • WMO GRIB2 data format.

Missing values

  • Bitmaps shall be used to indicate missing values.

Grid and resolution

  • Each partner will provide their eps data on a 0.25/0.25 regular lat-lon grid (1440x721 grid points, including poles).
  • First grid point is 90N 0E. The data will be archived first from west to east (OE to 358.5), and then from north to south (90N to 90S).
  • The related GRIB 2 meta data called scanning mode  should equal to 0.
    • Scanning mode 0

      • i scans positively (west to east)
        • i points are consecutive
      • j scans negatively (north to south)

  • The fields have to be provided on...
  • Grids are defined in GRIB2 using an accuracy of 1/1000000 (one millionth) of a degree.

Data compression

CCSDS compression should be used

GRIB2 encoding

All data must be encoded following the required rules described below to achieve fully compliant WPMIP format from all centres.

Encoding software

ECMWF makes available a GRIB decoding library (ecCodes) for the benefit of the WMO community. ecCodes can be freely downloaded from here and the documentation can be found here.

For more general information about GRIB2 format please refer to WMO Manual on Codes .

Encoding details

General encoding (TBA)

Specific details which should be encoded in GRIB2 sections 1 and 4:

Section 1
Octets Key nameValueDescriptionComments
6-7centreXWMO Centre's code (table below)
8-9subCentre0WMO Sub-Centre's code if needed (table below)only if needed
10tablesVersion36The latest WMO table*1
11localTablesVersion0Local tables not used
20productionStatusOfProcessedData16

Weather Prediction Model Intercomparison Project *2

use during production phase



17Weather Prediction Model Intercomparison Project *2use during testing phase
21typeOfProcessedData0Analysis products


1Forecast products

*1 New WMO tables version 36 (containing also new WPMIP keys) will be officialy released by WMO later in 2025 (November)

*2 New codes for the WPMIP (part of GRIB 2 tables version 36) to be approved by WMO by August 2025 (Manual on Codes (WMO-No. 306), Volume I.2, GRIB code table 1.3)

Section 4
Octets
Value (Example perturbed)Value (Example control)
8-9productDefinitionTemplateNumber

1/11*1

1/11*1

13backgroundProcess

1

1

14generatingProcessIdentifier

X*2

X*2

35typeOfEnsembleForecast255 (missing) 255 (missing) 
36perturbationNumber70
37numberOfForecastsInEnsemble5151

*1 statistically processed (typeOfStatisticalProcessing is set up)

*2 centre/model version dependent (see below)

Section 5
Octets
ValueDescription
10-11dataRepresentationTemplateNumber

42

[Grid point data - CCSDS recommended lossless compression (grib2/tables/29/5.0.table) ]


WMO Centre codes and model versions

WMO code key is used to identified each organisation.

If it is necessary to distinguish among more organizations (e.g. from the same country) using the same WMO code, the Sub-Centre key should be also deifned.

Model version for given centre is derived from following keys:

  • centre (unique for each provider)
  • backgroundProcess=1
  • generatingProcessIdentifier  (unique for each centre key)
OrganisationAcronymWMO Centre codeecCodes Centre acronym*1model versionecCodes model version acronym*1generatingProcessIdentifier value 

China Meteorological Administration, China

CMA
babj


European Centre for  Medium-Range Weather, UK

ECMWF98ecmf

1

v1

1





2

v2

2








Japan Meteorological Agency, JapanJMA34rjtd


National Centres for Environmental Prediction, USANCEP7kwbc


National Aeronautics and Space AdministrationNASA
nasa


Remarks:

*1 in ECMWF's ecCodes package

Examples of  the required GRIB2 files

parameter

Sample file


GRIB metadata dump*1







*1 using "grib_dump -O" command from ecCodes package