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Import type grib1 supports :
*importing ensembles,
*importing grid data from separate layers (z-dimension)
*importing grid data that are distributed over the several files, e.g. all forecasts in one file, one file per forecast, et cetera.
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Grib1 is an extension of import type 'NetcdfGridDataset' , which uses NetCdf as decoder.
See also (NetcdfGridDataset)