This page contains a few rules on the UERRA parameters. A complete list of all the parameters and GRIB2 encoding is given here.
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Units
- All fields shall use units as defined in GRIB Edition 2. The exact definition for each parameter is linked in Parameter page
Output frequency, levels for an/fc
- all details are available in Parameter page 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)
Parameters archived since previous post-processing
- Some parameters (2m tmin/tmax, 10m wind gust) shall be archived with varying length of time range intervals:
0-1/1-2/2-3/4-5/5-6/6-9/9-12/../27-30
Find further in this page GRIB2 files examples including header outputs etc
Fluxes
- The flux sign convention is positive downwards.
- Positive evaporation represents condensation.
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
- Each partner provide data on their native gridThe 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.
Ensemble type of outputs
- Ensemble member numbering must start from 1
Model levels
- Model level numbering must start from 1
GRIB2 encoding
ECMWF encoding/decoding Software
ECMWF makes available a GRIB decoding library (GRIB-API) for the benefit of the WMO community. GRIB-API 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
Info |
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The new GRIB-API version 1.19.0 which can recognise all UERRA parameters is already available on all ECMWF's premises (e.g. ecgate). Its official public release will follow soon in following weeks. |
UERRA-GRIB2 checking tool
The so called tigge_check tool is a part of GRIB-API package. It should be used to validate all GRIB2 files prepared for UERRA (the option -u). The tool is checking all encoding details so that only fully compliant UERRA files following exactly required definitions would pass. It can check also allowed value ranges for each parameter if used with the option -v. These ranges have not been fully defined for all UERRA parameters yet e.g. for radiation fluxes. Sometimes warnings about values exceeding expected limits do not mean error in the checked data but only model specific correct values.
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During the development phase there will be always the latest version of tigge_check tuned on the latest full sample data from providers available on ecgate: ecgate: ~marm/uerra/bin/tigge_check After the end of the development phase (when full samples for more days/weeks are available from all expected models) that last version of tigge_check will be added to the next closest official GRIB-API release. |
Examples of tigge_check usage:
Code Block |
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> module load grib_api/1.17.0
> load grib_api 1.17.0 Library (GRIB_API_MODE, GRIB_API_VERSION, GRIB_API_INCLUDE, GRIB_API_LIB, GRIB_API_INCLUDE_DIR, GRIB_API_LIB_DIR, EC_FFLAGS, EC_CFLAGS, EC_CXXFLAGS, EC_FLDFLAGS, EC_CLDFLAGS, EC_CXXLDFLAGS)
>
# example with one data value ranges warning and one encoding error
> tigge_check -u -w -v *.grib2
> warning: an.enda.tcw.sfc.0.fp.grib2, field 1 [total_column_water_sfc]: total_column_water_sfc maximum value 31.5638 is not in [50,150]
=> [31.5638,150]
> fc.oper.2t.sfc.2.grib2 , field 1 [temperature_hl]: invalid height level 3 |
WAVE-GRIB2 checking tool
TBD
GRIB2 encoding details
The complete WMO compliant GRIB2 definitions of all UERRA wave parameters are linked herein the parent page.
The additional generally required encoding UERRA details are listed below:
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Deterministic system (both analysis and forecast products)
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Ensemble DA system (both analysis and forecast products)
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37 | number of forecasts in ensemble | 4 |
Examples of UERRA compliant GRIB2 files
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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
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Time ( accumulated ) | ||||
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Start of forecast ( section 1 ) | ||||
Octets | Values | Meaning of values | Grib_api key | |
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 | |
Accumulation ( section 4 e.g. template 4.11 ) | ||||
18 | Indicator of unit of time range | 1 | Hour | |
19-22 | Forecast time | 0 | Accumulation starts at step=0 | startStep=0 |
38-39 | year of end of overall time interval | 2012 |
End of accumulated period, 20120103 06Z |
endStep=54
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40 | month of end of overall time interval | 01 | ||
41 | day of end of overall time interval | 03 | ||
42 | hour of end of overall time interval | 06 | ||
45 | number of time ranges | 1 | Only one type of time statistics used (accumulation) | |
46-49 | total number of data values missing in statistical process | 0 | ||
50 | Statistical process used to calculate the processed field from the field at each time increment during the time range | 1 | Accumulation | stepType=accum |
51 | Type of time increment between successive fields used in the statistical processing | 2 | Successive times processed have same start time of forecast, forecast time is incremented | |
52 | Indicator of unit of time for time range over which statistical processing is done | 1 | Hour | |
53-56 | Length of the time range over which statistical processing is done, in units defined by the previous octet | 54 |
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57 | Indicator of unit of time for the increment between the successive fields used | 255 | Missing | |
58-61 | Time increment between successive fields, in units defined by the previous octet | 0 | 0 |
Maximum since the previous post-processing
This example represents a maximum since the previous post-processing of a field valid on 20120103 00Z produced by a forecast started on 20120101 00Z . In this example, the maximum is the 6-hourly maximum in the time interval: steps 42 to 48.
- In bold, the values are fixed. They are meant to be used by all partners
- In green, these are the values for the example.
Time (Maximum over the last 6 hours ) | |||||||||||||
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Start of forecast ( section 1 ) | |||||||||||||
Octets | values | Meaning of values | Grib_api keys | 12 | Significance of Reference Time | 1 | Start of forecast | 13-14 | Year (four digits) | 2012year of start of forecast |
dataDate=20120101
dataTime=0
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End of maximum period
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endStep=48
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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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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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indicatorOfUnitForTimeIncrement=1
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Time increment between successive fields,
in units defined by the previous octet
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Minimum since the previous post-processing
This example represents a minimum since the previous post-processing of a field valid on 20120103 00Z produced by a forecast started on 20120101 00Z . In this example, the minimum is the 6-hourly minimum in the time interval: steps 42 to 48.
- 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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Fixed
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dataDate=20120101
dataTime=0
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End of minimum period
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endStep=48
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Statistical process used to calculate the processed field
from the field at each time increment during the time range
...
Type of time increment between successive fields
used in the statistical processing
...
Successive times processed have same start time of forecast, forecast time is incremented
...
Indicator of unit of time for time range
over which statistical processing is done
...
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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