| Table of Contents |
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Units
- All fields shall use units as defined in GRIB Edition 2.
Output frequency
- all details are available here
Accumulations
- All accumulations shall start from the beginning of the forecast
- The initial state (forecast step zero) must not be included (as it should be 0 value field by definition)
General requirements
Encoding format
- WMO GRIB2 data format.
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.
- 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
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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 (GRIB-APIecCodes) for the benefit of the WMO community. GRIB-API ecCodes can be freely downloaded from here and the documentation can be found here. The GRIB-API provides a simplified access to GRIB2 headers through a set of virtual keys documented here
WAVE-GRIB2 checking tool
TBD
GRIB2 encoding details
The complete WMO compliant GRIB2 definitions of all wave parameters are in the parent page.
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
General encoding
Specific details which should be encoded in GRIB2 sections 1 and 4The additional generally required encoding details are listed below:
| Section 1 | |||||||
|---|---|---|---|---|---|---|---|
| Octets | Key name | Value | Description | ||||
| 6-7 | centre | ||||||
| X | WMO Centre's code (table below) | ||||||
| 8-9 | subCentre | X | WMO Sub-Centre's code if needed (table below) | ||||
| 10 | tablesVersion | 19 | The latest WMO table | ||||
| 20 | productionStatusOfProcessedData |
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| 0 | Production data | ||
| 1 | Test data | ||||||
| 21 | typeOfProcessedData | 0 | Analysis products | ||||
| 1 | Forecast products | ||||||
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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)) |
| |||
Ensemble DA system (both analysis and forecast products)
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Value
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Description
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1
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Analysis and Forecast products (instantaneous)
(Individual ensemble forecast, control and perturbed, at a horizontal level or in a horizontal layer at a point in time (grib2/tables/17/4.0.table))
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Analysis and Forecast products (statistically processed = accumulated/min/max values)
(Individual ensemble forecast, control and perturbed, at a horizontal level or in a horizontal layer, in a continuous or non-continuous time interval (grib2/tables/17/4.0.table))
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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 | WMO subCentre code | Centre acronym*1 |
|---|---|---|---|---|
European Centre for Medium-Range Weather, UK | ECMWF | 98 | N/A | ecmf |
| Met office, UK | UKMO | 74 | N/A | egrr |
| Fleet Numerical Meteorology and Oceanography Center, USA | FNMOC | 58 | N/A | fnmo |
| Environment and Climate Change Canada, Canada | ECCC | 54 | N/A | cwao |
| National Centres for Environmental Prediction, USA | NCEP | 7 | N/A | kwbc |
| Météo France, France | METFR | 84 | N/A | lfpw |
| Deutscher Wetterdienst, Germany | DWD | 78 | N/A | edzw |
| Bureau of Meteorology, Australia | BoM | 1 | N/A | ammc |
| Laboratoire D'Océanographie Physique et Spatiale, France | LOPS | 84 | 202 | lops |
| Japan Meteorological Agency, Japan | JMA | 34 | N/A | rjtd |
| Korea Meteorological Administration, Republic of Korea | KMA | 40 | N/A | rksl |
| Puertos del Estado, Spain | PRTOS | 214 | N/A | lemm |
| Danmarks Meteorologiske Institut, Denmark | DMI | 94 | N/A | ekmi |
National Institute of Water and Atmospheric Research, New Zealand | NIWA | 204 | N/A | niwa |
Det Norske Meteorologiske Institutt, Norway | METNO | 88 | N/A | enmi |
Servicio de Hidrografía Naval, Servicio Meteorológico, Argentina | SHNSM | 41 | N/A | sabm |
New Zealand MetService | NZMS | 69 | N/A | nzkl |
| Servizio Meteorologico dell'Aeronautica Militare, Italy | METEOAM | 80 | N/A | cnmc |
Remarks:
*1 in ECMWF's eCcodes
Example of the validity type encoding
Examples of UERRA compliant GRIB2 files
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Accumulations
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Instantaneous on surface level
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Instantaneous on model level
(Specific humidity on model level 1)
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Maximum since previous post-processing
(Surface air maximum temperature since previous post-processing)
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grib*
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Minimum since previous post-processing
(Surface air minimum temperature since previous post-processing)
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Parameter on soil level
(Soil temperature on soil level 1)
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*disregard data values in this grib (some step/level values were created artificially as real data has not been available yet)
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Instantaneous
This example describes an instantaneous field valid on 20120103 00Z from a forecast starting on 20120101 00Z (time step=48 hours) .
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| 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
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| 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 | |
Accumulations
This example represents a 54 hour accumulation of a field produced by a forecast started on 20120101 00Z.
- 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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Examples of the required GRIB2 files
parameter | Sample file |
|---|---|
10 metre U wind component | wave.10u.grib2 |
10 metre V wind component | wave.10v.grib2 |
| Mean wave period based on second moment | wave.mp2.grib2 |
| Mean wave direction | wave.mwd.grib2 |
| Peak wave period | wave.pp1d.grib2 |
Significant height of combined wind waves and swell | wave.swh.grib2 |
dataDate=20120101
dataTime=0
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End of accumulated period, 20120103 06Z
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endStep=54
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Statistical process used to calculate the processed
field from the field at each time increment during the time range
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stepType=accum
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Type of time increment between successive fields used in the statistical processing
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Successive times processed have same start time of forecast,
forecast time is incremented
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Indicator of unit of time for time range over which statistical processing is done
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Length of the time range over which statistical processing is done,
in units defined by the previous octet
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Indicator of unit of time for the increment between the successive fields used
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Time increment between successive fields, in units defined by the previous octet
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