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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 GRIB Edition 2. WMO GRIB2 manual
Output frequency (TBD)
- 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)
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)
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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
TBD
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
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details
The complete WMO compliant GRIB2 definitions of all wave parameters are linked in the parent page .The additional generally required Wave verification
General encoding details
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| Section 1 | |||||||
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| Octets | Key name | Value | Description | ||||
| 6-7 | centre | ||||||
| TBD | only in local section i.e. not here? | ||||||
| 10 | tablesVersion | latest WMO table with some new definitions for UERRA | |||||
| 20 | productionStatusOfProcessedData | operational UERRA products | |||||
wave verification products | |||||||
| 21 | typeOfProcessedData | 1 | Forecast products | ||||
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| Section 4 | |||||||
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| 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)) |
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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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Example
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of the validity type encoding
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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)
Examples of encoding for various parameter validity types
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 |
| 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 |
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10 metre U wind component | WAVE_165.128_1x1.grb2 |
10 metre V wind component | WAVE_166.128_1x1.grb2 |
| Mean wave period based on second moment | WAVE_221.140_1x1.grb2 |
| Mean wave direction | WAVE_230.140_1x1.grb2 |
| Peak wave period | WAVE_231.140_1x1.grb2 |
Significant height of combined wind waves and swell | WAVE_229.140_1x1.grb2 |
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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