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• 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.
• 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. 

Directory structure of static sample dataset

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

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<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/scdawaef ├──└── anpf │   ├── ml │   ├── pl │   ├── pt │   ├── pv└── sfc <root_dir>/od/wave ├── an │   ├── └── sfc │   └── sol └── fc ├──└── ml ├── pl ├── pt ├── pv ├── sfc └── sol <root_dir>/od/scwv ├── an │   └── sfc └── fc └── sfc <root_dir>/od/waef └── pf └── sfc <root_dir>/od/wave ├── an │  └── sfc └── fc └── sfc sfc

Structure of file namesStructure of filenames

Each directory at the end of the tree contains one file per parameter containing all forecast time steps.  The files are named <paramId>_<class>_<stream>_<type>_<levtype>_<shortName>_<year>_<expver>_<gridType>.grib2 and are based on the ecCodes paramId, shortName and gridType and the MARS class, stream, type, levtype used for the current operational output at IFS cy49r1.

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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. having level=2. 

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To retrieve these parameters in GRIB2 from MARS, users will need to use the new paramId and also specify the statistical processing time window using a new MARS keyword - timespan - that is to be introduced. 

Maximum 10m wind gust

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Maximum and minimum 2m temperature

Maximum and minimum total precipitation rate

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Maximum CAPE and CAPE Shear

Mean total lightning flash density

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Most severe and most frequent precipitation type

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• 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.

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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.

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