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 name | Value | Description |
| 6-7 | centre | X | WMO Centre's code (table below) |
| 8-9 | subCentre | 0 | WMO Sub-Centre's code if needed (table below) |
| 10 | tablesVersion | 35 | The latest WMO table*1 |
| 20 | productionStatusOfProcessedData | 14 | Lead Centre for Global Climate Reanalyses *2 |
| 15 | Lead Centre for Global Climate Reanalyses test *2 | ||
| 21 | typeOfProcessedData | 0 | Analysis products |
| 1 | Forecast 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 | |||
|---|---|---|---|
| Octets | Key name | Value | Description |
| 8-9 | productDefinitionTemplateNumber | 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.
| Organisation | Acronym | WMO Centre code | Centre acronym*1 |
|---|---|---|---|
China Meteorological Administration, China | CMA | babj | |
European Centre for Medium-Range Weather, UK | ECMWF | 98 | ecmf |
| Japan Meteorological Agency, Japan | JMA | 34 | rjtd |
| National Centres for Environmental Prediction, USA | NCEP | 7 | kwbc |
| National Aeronautics and Space Administration | NASA | 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.grib2 | ecmf.an.txt |
Time-mean mean sea level pressure | ||
| Time-mean total precipitation | ecmf.fc.grib2 | ecmf.fc.txt |
*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
- for example exact encoding of time ranges will differ for different models depending on how daily sums are constructed etc
- 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
- currently it supports mainly centre=ecmf