Gridded data in NetCDF format

Gridded, structured data can be read from NetCDF files that follow the Climate and Forecast (CF) Metadata Conventions. Define a dataset consisting of CF-compliant NetCDF files by selecting "File→New Dataset" in the Met.3D main window, or alternatively, by adding the following entry to your user-defined pipeline.cfg file (cf. https://gitlab.com/wxmetvis/met.3d/-/blob/master/config/default_pipeline.cfg.template):

1\name=YOUR DATASET NAME
1\path=/your/path/data/netcdf
1\fileFilter=*ecmwf_ensemble_forecast*EUR_LL10*.nc
1\schedulerID=MultiThread
1\memoryManagerID=NWP
1\fileFormat=CF_NETCDF
1\enableRegridding=true

All files in the specified path that match the given file filter will be used for the dataset. See the file default_pipeline.cfg.template (https://gitlab.com/wxmetvis/met.3d/-/blob/master/config/default_pipeline.cfg.template) for further comments on the meaning of the individual keywords.

The following example contains a NetCDF header of a file containing an ensemble forecast on pressure levels:

netcdf somegriddeddata.pl {
dimensions:
    lon = 101 ;
    lat = 41 ;
    isobaric = 12 ;
    time = 1 ;
    ens0 = 51 ;
variables:
    float lat(lat) ;
            lat:units = "degrees_north" ;
    float lon(lon) ;
            lon:units = "degrees_east" ;
    float isobaric(isobaric) ;
            isobaric:units = "hPa" ;
            isobaric:long_name = "Isobaric surface" ;
            isobaric:positive = "down" ;
    int time(time) ;
            time:units = "Hour since 2012-10-15T00:00:00.000Z" ;
            time:standard_name = "time" ;
    int ens0(ens0) ;
            ens0:standard_name = "ensemble_member_id" ;

    float Geopotential_isobaric(time, ens0, isobaric, lat, lon) ;
            Geopotential_isobaric:long_name = "Geopotential @ Isobaric surface" ;
            Geopotential_isobaric:units = "m2.s-2" ;
    float Temperature_isobaric(time, ens0, isobaric, lat, lon) ;
            Temperature_isobaric:long_name = "Temperature @ Isobaric surface" ;
            Temperature_isobaric:units = "K" ;

    ...
}

• The latitude and longitude dimensions are recognised according to their units keyword; cf. the longitude/latitude section in CF-conventions.

• The vertical pressure level dimension requires units of pressure, as well the positive attribute being defined; cf. the vertical coordinate section in CF-conventions.

• Time time dimension is identified by its units attribute; cf. the time coordinate section in CF-conventions.

The following example contains a NetCDF header of a file containing an ensemble forecast on hybrid sigma-pressure levels; the required keyword of the vertical variable are different; cf. Appendix D of the CF-conventions.

netcdf somegriddeddata.ml {
dimensions:
    lon = 101 ;
    lat = 41 ;
    hybrid = 62 ;
    time = 1 ;
    ens0 = 51 ;
variables:
    float lat(lat) ;
            lat:units = "degrees_north" ;
    float lon(lon) ;
            lon:units = "degrees_east" ;
    float hybrid(hybrid) ;
            hybrid:units = "sigma" ;
            hybrid:long_name = "Hybrid level" ;
            hybrid:positive = "down" ;
            hybrid:standard_name = "atmosphere_hybrid_sigma_pressure_coordinate" ;
            hybrid:formula = "p(time,level,lat,lon) = ap(level) + b(level)*ps(time,lat,lon)" ;
            hybrid:formula_terms = "ap: hyam b: hybm ps: Surface_pressure_surface" ;
    int time(time) ;
            time:units = "Hour since 2012-10-15T12:00:00.000Z" ;
            time:standard_name = "time" ;
    int ens0(ens0) ;
            ens0:_CoordinateAxisType = "Ensemble" ;

    double hyam(hybrid) ;
            hyam:long_name = "hybrid A coefficient at layer midpoints" ;
            hyam:units = "Pa" ;
    double hybm(hybrid) ;
            hybm:long_name = "hybrid B coefficient at layer midpoints" ;
            hybm:units = "1" ;

    float Temperature_hybrid(time, ens0, hybrid, lat, lon) ;
            Temperature_hybrid:long_name = "Temperature @ Hybrid level" ;
            Temperature_hybrid:units = "K" ;
    float Specific_humidity_hybrid(time, ens0, hybrid, lat, lon) ;
            Specific_humidity_hybrid:long_name = "Specific humidity @ Hybrid level" ;
            Specific_humidity_hybrid:units = "kg/kg" ;

    ...
}

Gridded data in GRIB format

Met.3D provides support for GRIB files written by ECMWF’s ecCodes library (as output, e.g. by the ECMWF MARS archive or written by Metview).

In your pipeline.cfg file, simply change the fileFormat entry to ECMWF_GRIB:

1\name=YOUR DATASET NAME
1\path=/your/path/data/grib
1\fileFilter=*ecmwf_ensemble_forecast*EUR_LL10*.grb
1\schedulerID=MultiThread
1\memoryManagerID=NWP
1\fileFormat=ECMWF_GRIB
1\enableRegridding=true

• GRIB messages may be arbitrarily distributed over different files that match the specified fileFilter.
• Support is currently only provided for a horizontally regular longitude/latitude grid (GRIB gridType = regular_ll) and either pressure (GRIB typeOfLevel = isobaricInhPa) or hybrid sigma-pressure levels (GRIB typeOfLevel = hybrid) in the vertical.
• Hybrid sigma-pressure model levels additionally require the surface pressure field (GRIB shortName = sp) or its logarithm (GRIB shortName = lnsp) to be present in the dataset.
• Analysis (GRIB dataType = an), forecast (GRIB dataType = fc) and perturbed/control (i.e., ensemble forecast; GRIB dataType = pf/cf) messages are interpreted.
• For 3D fields, a consistent consecutive list of vertical levels must be present for all time steps and ensemble members of a dataset. Levels need not be complete (i.e., there can be missing levels at the top or bottom) but the same levels need to be provided for all data fields in a dataset.
• For a given dataset, all GRIB messages must have the same horizontal extent.