General requirements

Encoding format

• Participating Centres are expected to produce output fields in 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 (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

ECMWF encoding/decoding 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

WAVE-GRIB2 checking tool

Tool for checking input file compliance with the agreed GRIB2 format; any other additional checks (geometry, basic data quality i.e. allowed extremes check etc)? TBD

Encoding details

The complete WMO compliant GRIB2 definitions of all wave parameters are linked in the page Wave verification

General encoding details

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.

Examples of  the required GRIB2 files