The data if available on spectral grid or gaussian grid, then it needs to be remapped onto a regular lat lon grid, so that it can be analysed using Met.3D. The following code snippet outlines the steps to do this remapping.
#!/bin/bash
#####################################################################################
# Minimal examples of basic CDO commands for remapping ERA5 data on a regular grid
# which can be loaded into Met.3D for interactive 3-D visual analysis
#
# (Marcel Meyer, Visual Data Analysis, Regional Computing Center, UHH, 2020)
#
#
# Link to the Met.3D documentation
# https://collaboration.cen.uni-hamburg.de/display/Met3D/Welcome+to+Met.3D
#
# Link to the cdo documentation
# https://code.mpimet.mpg.de/projects/cdo/wiki/Cdo#Documentation
#
# Link to a cdo reference sheet
# https://code.mpimet.mpg.de/projects/cdo/embedded/cdo_refcard.pdf
#
#####################################################################################
###########
# define path to the folder storing the ERA5 data as provided by the ECMWF
# (GRIB data with spatial coordinate systems "Gaussian Grid" or "Spherical Harmonics")
DATAFOLDER=/path/to/ERA5-data-folder/
##########
# define path to the folder for storing the remapped ERA5 data-files
POSTPROCESSEDDATAFOLDER=/path/to/Results-Folder/
mkdir -p ${POSTPROCESSEDDATAFOLDER}
##########
# define path to a file characterizing the grid to which the ERA5 data will be remapped
TARGETGRIDFILE=/path/to/targetgridfile.txt
# examplar gridFile for remapping with CDO to a regular lat-lon grid :
# --> "cdo_gridFile_regular_LatLon_minimalExample.txt"
##########
# define input and output data files
INFILE=/path/to/ERA5_Data_File
OUTFILE=/path/to/ERA5_Data_on_regular_grid
##########
# bilinear remapping from reduced Gaussian grid to regular Lat-Lon grid
# and conversion from GRIB to NETCDF
cdo -f nc4 -remapbil,${TARGETGRIDFILE} -setgridtype,regular ${OUTFILE} ${INFILE}
##########
# bilinear remapping from spectral grid to Gaussian grid to regular Lat-Lon grid
cdo -f nc4 -remapbil,${TARGETGRIDFILE} -sp2gpl ${INFILE} ${OUTFILE}
The contents of the 'cdo_gridFile_regular_LatLon_minimalExample.txt' in this example are as below:
gridtype = lonlat gridsize = 90381 xsize = 641 ysize = 141 xfirst = -80 xinc = 0.25 yfirst = 85 yinc = -0.25