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. EcCodes provides a simplified access to GRIB2 headers through a set of virtual keys documented here.
For more general information about GRIB2 format please refer to WMO Manual on Codes .
Encoding details
Parameters
- 10 metre U wind component
- 10 metre V wind component
- Mean wave direction
- Mean zero-crossing wave period
- Peak wave period
- Significant height of combined wind waves and swell
General encoding
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 | WMO subCentre code | Centre acronym*1 |
|---|---|---|---|---|
European Centre for Medium-Range Weather, UK | ECMWF | 98 | N/A | ecmf |
| Met office, UK | UKMO | 74 | N/A | egrr |
| Fleet Numerical Meteorology and Oceanography Center, USA | FNMOC | 58 | N/A | fnmo |
| Environment and Climate Change Canada, Canada | ECCC | 54 | N/A | cwao |
| National Centres for Environmental Prediction, USA | NCEP | 7 | N/A | kwbc |
| Météo France, France | METFR | 84 | N/A | lfpw |
| Deutscher Wetterdienst, Germany | DWD | 78 | N/A | edzw |
| Bureau of Meteorology, Australia | BoM | 1 | N/A | ammc |
| Laboratoire D'Océanographie Physique et Spatiale, France | LOPS | 84 | 202 | lops |
| Japan Meteorological Agency, Japan | JMA | 34 | N/A | rjtd |
| Korea Meteorological Administration, Republic of Korea | KMA | 40 | N/A | rksl |
| Puertos del Estado, Spain | PRTOS | 214 | N/A | lemm |
| Danmarks Meteorologiske Institut, Denmark | DMI | 94 | N/A | ekmi |
National Institute of Water and Atmospheric Research, New Zealand | NIWA | 204 | N/A | niwa |
Det Norske Meteorologiske Institutt, Norway | METNO | 88 | N/A | enmi |
Servicio de Hidrografía Naval, Servicio Meteorológico, Argentina | SHNSM | 41 | N/A | sabm |
New Zealand MetService | NZMS | 69 | N/A | nzkl |
| Servizio Meteorologico dell'Aeronautica Militare, Italy | METEOAM | 80 | N/A | cnmc |
Remarks:
*1 in ECMWF's eCcodes
Example of the validity type encoding
Instantaneous
This example describes an instantaneous field valid on 20120103 00Z from a forecast starting on 20120101 00Z (time step=48 hours) .
- In bold, the values are fixed. They are meant to be used by all partners
- In green, these are the values for the example.
| Time ( instantaneous ) | ||||
|---|---|---|---|---|
| Start of forecast ( section 1 ) | ||||
Octets | values | Meaning of values | Grib_api values | |
| 12 | Significance of Reference Time | 1 | Start of forecast | |
| 13-14 | Year (four digits) | 2012 | year of start of forecast |
dataDate=20120101 dataTime=0 |
| 15 | Month | 01 | month of start of forecast | |
| 16 | Day | 01 | day of start of forecast | |
| 17 | Hour | 00 | hour of start of forecast | |
| section 4 e.g. template 4.1 | ||||
| 18 | Indicator of unit of time range | 1 | Hour | |
| 19-22 | Forecast time | 48 | Forecast step | stepType=instant, step=48 |
Examples of the required GRIB2 files
parameter | Sample file |
|---|---|
10 metre U wind component | wave.10u.grib2 |
10 metre V wind component | wave.10v.grib2 |
| Mean wave period based on second moment | wave.mp2.grib2 |
| Mean wave direction | wave.mwd.grib2 |
| Peak wave period | wave.pp1d.grib2 |
Significant height of combined wind waves and swell | wave.swh.grib2 |