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General requirements
Encoding format
- Participating Centres are expected to produce output fields in WMO GRIB2 data format and with consistent units. For more information please refer to WMO Manual on Codes
Parameters
Units
- All fields shall use units as defined in WMO Tables
Output frequency
- The model output steps should be between 1 and 12 hour
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
The complete WMO compliant GRIB2 definitions of all wave parameters are linked in the page LC-WFV technical details
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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:
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