DRS Template 5.42

[ghassan-alaka]

Describe the bug ECMWF recently upgraded the GRIB2 compression method to CCSDS (using data representation template 5.42). This is resulting in an error while attempting to read ECMWF-produced GRIB2 files in NCL. NCL does not exit with this error, but my script quickly fails because no GRIB2 data is actually read. The full error is:

getdrstemplate: DRS Template 5.42 not defined.
warning:Error unpacking GRIB record section 5.

Provide the following:

• NCL script:

  f=addfile("/DATA/PATH/20230627120000-0h-oper-fc.grib2","r")
  print(f)

  • example data file https://data.ecmwf.int/forecasts/20230627/12z/0p4-beta/oper/20230627120000-0h-oper-fc.grib2

Computing environment

• OS: Linux (NOAA)
• OS version: CentOS Linux 7 (Core)
• NCL Version: 6.6.2
• Installation method: binary from NCAR website

Additional context I think this problem might be resolved by adding the correct table information in this sub-directory, but I'm not sure exactly what to change/add: ${NCARG_ROOT}/lib/ncarg/grib2_codetables/ecmwf/5/

I am in the process of migrating from NCL to Python. It would be nice to continue to process ECMWF data using NCL until that migration is complete.

[ghassan-alaka]

NCL uses g2clib to read GRIB2. Does anyone know if g2clib can currently handle the CCSDS compression method? If so, how would I make that updated library available in NCL v6.6.2?

[cacraig]

Found this on a google search, as I ran into this issue as well (not with NCL, but with GDAL). Looks like you can use the ecCodes tool to decompress the data and get it into a usable format by NCL or GDAL or whatever.

grib_set -r -w packingType=grid_ccsds -s packingType=grid_simple ccsds_compressed_grib.grib output.grib

Hope this workaround helps you, and other strangers that search for this issue.