General requirements
Encoding format
Units
Output frequency
- The model output steps should be between 1 and 12 hour
Missing values
- Bitmaps shall be used to indicate missing values (i.e. Soil temperature (st) shall be coded using a bitmap, because there is no model output over the sea)
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.
GRIB2 encoding
Encoding software
ECMWF makes available a GRIB decoding library (ecCodes) for the benefit of the WMO community. The 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
Encoding details
The complete WMO compliant GRIB2 definitions of all wave parameters are linked in the page Wave verification
General encoding details
| Section 1 |
|---|
| Octets | Key name | Value | Description | | 6-7 | centre | X | Centre's code (next table) | | 8-9 | subCentre | X | If centre is not sufficient (next table) | | 10 | tablesVersion | 19 | latest WMO table | | 20 | productionStatusOfProcessedData | 0 | Operational products | | | | 1 | Operational test products | | 21 | typeOfProcessedData | 1 | Forecast products |
|
asdfaCentre codes (WMO Manual 306 - WMO Codes)| | Organisation | Acronym | centre | value | subCentre | value | description |
|---|
| 1 | European Centre for Medium-Range Weather | ECMWF | | | N/A | N/A | ECMWF (RSMC) | | 2 | Met office, UK | UKMO | | | | | | | 3 | Fleet Numerical Meteorology and Oceanography Centre, USA | FNMOC | | | | | | | 4 | Environment and Climate Change Canada, Canada | ECCC | | | | | | | 5 | National Centres for Environmental Prediction, USA | NCEP | | | | | | | 6 | Météo France, France | METFR | | | | | | | 7 | Deutscher Wetterdienst, Germany | DWD | | | | | | | 8 | Bureau of Meteorology, Australia | BoM | | | | | | | 9 | Service Hydrographique et Océanographique de la Marine, France | SHOM |
| | | | | | 10 | Japan Meteorological Agency, Japan | JMA | | | | | | | 11 | Korea Meteorological Administration, Republic of Korea | KMA | | | | | | | 12 | Puertos del Estado, Spain | PRTOS | | | | | | | 13 | Danmarks Meteorologiske Institut, Denmark | DMI | | | | | | | 14 | National Institute of Water and Atmospheric Research, New Zealand | NIWA | | | | | | | 15 | Det Norske Meteorologiske Institutt, Norway | METNO | | | | | | | 16 | Servicio de Hidrografía Naval, Servicio Meteorológico, Argentina | SHNSM | | | | | | | 17 | New Zealand MetService | NZMS | | | | | | | 18 | Servizio Meteorologico dell'Aeronautica Militare, Italy | METEOAM | | | | | |
nazdar |
| 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)) |
Example of the validity type encoding
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