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 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

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

GRIB2 encoding

All data must be encoded following the required rules described below to achieve fully compliant LC-GCR 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 nameValueDescription
6-7centreXWMO Centre's code (table below)
8-9subCentre0WMO Sub-Centre's code if needed (table below)
10tablesVersion35The latest WMO table*1
20productionStatusOfProcessedData14

Lead Centre for Global Climate Reanalyses *2



15Lead Centre for Global Climate Reanalyses test *2
21typeOfProcessedData0Analysis products


1Forecast products

*1 New WMO tables version 35 (containing also new LC-GCR keys) will be officialy released by WMO later in 2025 (May-June)

*2 New codes for the LC-GCR (part of GRIB 2 tables version 35) approved by WMO in January 2025 (Manual on Codes (WMO-No. 306), Volume I.2, GRIB code table 1.3)

Section 4
OctetsKey name

Value

Description

8-9productDefinitionTemplateNumber

0

Analysis and Forecast products (instantaneous)

(Analysis or forecast at a horizontal level or in a horizontal layer at a point in time (grib2/tables/17/4.0.table))

WMO Centre codes

The codes below are based on WMO Manual 306 - WMO Codes. Each organization must be uniquely identified by its WMO code. If necessary to distinguish between two organizations using the same WMO code the Sub-Centre one which differs must be provided.

OrganisationAcronymWMO Centre codeCentre acronym*1

China Meteorological Administration, China

CMA
babj

European Centre for  Medium-Range Weather, UK

ECMWF98ecmf
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

Time-mean 2 metre temperature

ecmf.an.grib2ecCodes output

Time-mean mean sea level pressure

Time-mean total precipitationecmf.fc.grib2ecCodes output

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

Remarks

  • sample files ecmf.*.grib2 files come from ECMWF's IFS model (data based on the current ERA5)
  • ecCodes Version 2.40.0 should be used to display correctly some LC-GCR related meta data 
    • currently it supports mainly centre=ecmf 
      • support for other participating models (centre=babj/rjtd/kwbc/nasa) can be added only once we understand full details, how reanalyses are produced by the providers
        • exact encoding of time ranges will differ for different models depending on how daily sums are constructed etc
          • for example following applies to ERA5:
            • Analysis are produced 1-hourly for 0-23h
            • Average accumulations within a particular day=date  are the average from the following forecasts:
              • date-1    18UTC, step=7/to/12/by/1
              • date        06UTC, step=1/to/12/by 1
              • date       18UTC  step=1/to/6/by/1



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