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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 Guide to the WMO Table Driven Code Form.

Units

• All fields shall use units as defined in WMO GRIB2 manual

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. 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.

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 Wave verification

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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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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 to two organizations using the same WMO code the Sub-Centre one which differs must be provided.

Remarks:

*1 in ECMWF's eCcodes

Example of the validity type encoding

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