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- GRIB messages may be arbitrarily distributed over different files that match the specified
fileFilter. - As for NetCDF files, support is 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 field (GRIB shortName =
sp) or its logarithm (GRIB shortName =lnsp) to be present in the dataset (GRIB shortName =sp). - 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.
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Unlike NetCDF files, GRIB files do not contain global headers that summarize the information contained in the file. Hence, to know which data is stored in a file the entire file needs to be read. This, of course, is inefficient when the file is accessed multiple times from different Met.3D sessions. Met.3D hence creates index files that store such a "global header" when first accessing GRIB files. You will find these files along with the GRIB files in the directory in which the GRIB files are stored. Note that your user ID hence requires write access to the directory in which the GRIB files are stored. If you don't have write access, we recommend placing symlinks to the files in a directory to which you have access and in which the index files can be stored. |