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Contents of the sample static dataset

To help users begin planning for the migration, we have produced an initial static sample dataset which provides sample data encoded in GRIB edition 2 from: 

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Sample data encoded in GRIB2 from the ensemble post-processed products (ensemble mean, maximum, etc, EFI and Sot), ensemble hindcasts, sub-seasonal and sub-seasonal hindcasts will also be made available in due course.

The sample data are based on the output from the current IFS cy49r1 output for the 00 UTC cycle on 30 November 2024 but encoded in GRIB2 as we currently expect the data which will be produced by IFS cy51r1 are currently expected to be encoded.  All fields provided are global and interpolated to a 1.0° x1.0° regular latitude-longitude grid.

• Data on constant pressure levels (type=pl) are provided at level=100 only.
  
• Data on theta levels (type=pt) are provided at level=300 for type=fc and level=265 only for type=an.
• Data on potential vorticity levels (levtype=pv) are provided at level=1500 only.
• Data on model levels (levtype=ml) are provided at level=1 only.
• Parameters accumulated from the start of the forecast have the ecCodes startStep key consistently set to 0 and, consequently, stepRange=0-24 in GRIB2 compared to stepRange=24, etc, in GRIB1
• Parameters accumulated from the start of the forecast are not provided at stepRange=0. 

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Where to obtain the static sample dataset

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• Users with login access to the ECMWF HPC service can access the data from the directory /ec/vol/mtg2_sample

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• . 
• Users without login access to the ECMWF HPC or ECS service can download the data from https://data.ecmwf.int/mtg2_sample.

Directory structure of static sample dataset

Data are ordered in a MARS-like folder structure under <root_dir>/<class>/<stream>/<type>/<levtype>.  Shown below is a diagrammatic layout of the structure under <root_dir>=/ec/vol/mtg2_sample/: 

<root_dir>/od/enfo
└── pf
 

<root_dir>/od/enfo
└── pf
    ├── pl
    ├── pt
    ├── pv
    ├── sfc
    └── sol

<root_dir>/od/oper
├── an
│   ├── ml
│   ├── pl
│   ├── pt
│   ├── pv
│   ├── sfc
│   └── sol
└── fc
    ├── ml
    ├── pl
    ├── pt
    ├── pv
    ├── sfc
    └── sol

<root_dir>/od/waef
└── pf
    └── sfc

<root_dir>/od/wave
├── an
│   └── sfc
└── fc
    └── sfc

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In general, the static sample dataset  is not suitable for initialising an NWP model.  Although encoding examples of all parameters at all forecast steps are available, for those parameters on constant pressure levels, for example, only the 1hPa level is provided.  However, users that initialise NWP models from ECMWF data should note the change in the way the parameters on soil levels are provided as this may require changes to your code.  Instead of having four separate parameters at each soil layer, in GRIB2 there will be one parameter available at each of the four layers (levels).

Changes to encoding of parameter paramId, shortName, name and units

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Although encoding examples of all parameters at all forecast steps are available, for those parameters on constant pressure levels, for example, only the 1hPa level is provided.  However, users that initialise NWP models from ECMWF data should note the change in the way the parameters on soil levels are provided as this may require changes to your code.  Instead of having four separate parameters at each soil layer, in GRIB2 there will be one parameter available at each of the four layers (levels).

Other sources of ECMWF GRIB2 data that can be used for testing

Along with the static sample dataset, users can also use the ECMWF Open Data to test their processing of GRIB2 data.  All of the open data are encoded in GRIB2.  For more information about these data and how to obtain them, see ECMWF open data: real-time forecasts from IFS and AIFS.

Changes to encoding of parameter paramId, shortName, name and units

The encoding of the ecCodes paramId, shortName, name and units have changed for some surface parameters from the analysis and forecast.  Users may need to adapt their workflows in order to process these parameters successfully.  The main changes affecting parameters provided in the static sample dataset are summarised below.  For a list of all changes to parameter encoding, see

Soil temperature, volumetric soil moisture and sea-ice temperature

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For example, in GRIB1, there is a paramId for Volumetric soil water layer 1 and a different paramId for Volumetric soil water layer 2, etc.  In GRIB2, only a single paramId is used for Volumetric soil water, with the layer 1 having level=1 and layer 2 having level=2. 

These parameters will be archived in MARS with levtype=sol (surface other levels).  To retrieve these parameters in GRIB2, users will need to change their MARS requests to specify levtype=sol,levelist=1/2/3/4.

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Maximum 10m wind gust

Maximum and minimum 2m temperature

Maximum and minimum total precipitation rate

Maximum CAPE and CAPE Shear

Mean total lightning flash density

Most severe and most frequent precipitation type

Ocean model output

The paramId's and shortNames for the following output from the ocean model have changed.  In addition:

• the unit of Sea surface practical salinity and Average sea water practical salinity in the upper 300 m has changed from psu to g/kg;
• the unit of the Average sea water potential temperature in the upper 300m has changed from degrees Celsius to Kelvin.

Fluxes of chemical species

In GRIB1, parameters that are fluxes of chemical species have different paramIds for each chemical species and type of flux.  In GRIB2, a unique paramId indicates the type of flux and a new key called chemShortName identifies the chemical.  For example, paramId=435000 refers to the Net ecosystem exchange flux and the chemShortName=CO2 identifies this as the Carbon dioxide net ecosystem exchange flux.

To retrieve these parameters in GRIB2 from MARS, users will need to use the new paramId and also specify the chemical species using the MARS keyword, chem.