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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
- 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
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- TBA
General encoding (TBA)
Specific details which should be encoded in GRIB2 sections 1 and 4:
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| 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 Institute of Water and Atmospheric Research, New Zealand
Det Norske Meteorologiske Institutt, Norway
Servicio de Hidrografía Naval, Servicio Meteorológico, Argentina
New Zealand MetService
| National Aeronautics and Space Administration | NASA | nasa |
Remarks:
*1 in ECMWF's eCcodesecCodes package
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.
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Octets
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values
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dataDate=20120101
dataTime=0
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Examples of the required GRIB2 files
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parameter
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10 metre U wind component
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10 metre V wind component
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Significant height of combined wind waves and swell
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