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 a regular latitude‐longitude grid at the resolution that is best matching the native resolution of the direct model output.
- Grids are defined in GRIB2 using an accuracy of 1/1000000 (one millionth) of a degree.
- If several limited areas will be provided they should be merged into one larger area on a regular lat-lon grid, with a missing value indicator in the grid-points not covered.
GRIB2 encoding
All data must be encoded following the required rules described below to achieve fully compliant LC-WFV 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
Parameters
- TBA
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 | X | WMO Sub-Centre's code if needed (table below) |
| 10 | tablesVersion | 19 | The latest WMO table |
| 20 | productionStatusOfProcessedData | 0 | Production data |
| 1 | Test data | ||
| 21 | typeOfProcessedData | 0 | Analysis products |
| 1 | Forecast products | ||
| 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