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Version 5.1.9 of the netCDF Operators (NCO) has been released. NCO is an Open Source package that consists of a dozen standalone, command-line programs that take netCDF files as input, then operate (e.g., derive new data, average, print, hyperslab, manipulate metadata) and output the results to screen or files in text, binary, or netCDF formats.

The NCO project is coordinated by Professor Charlie Zender of the Department of Earth System Science, University of California, Irvine. More information about the project, along with binary and source downloads, are available on the SourceForge project page.

From the release message:

Version 5.1.9 updates ncremap to employ new TempestRemap weight-generation algorithms (bilinear and integrated bilinear), updates ncremap to recognize new names for existing algorithms, changes ncremap's default treatment of filling empty areas with missing values, and fixes a long-standing bug with ncra and ncrcat subcycle and interleave options. A notable fix for MS Windows OS is included as are a few other miscellaneous features and fixes described below.

New Features

1. ncremap supports a new flag, --mpt_mss, to control the values placed in empty unmasked destination gridcells in sub-gridscale (SGS) mode. SGS mode interprets every gridcell as being fractionally covered by an amount contained in sgs_var (e.g., landfrac, seaicefrac). Empty in this context means unmasked cells where sgs_var is zero, e.g., no land, or no sea ice. Since ~2020, ncremap has filled empty SGS cells with the missing value. NCO 5.1.9 changes that behavior so that, by default, empty SGS cells are filled with zeros. This makes maps of sea-ice variables, e.g., zero in open ocean and non-zero where sea ice exists. Users can explicitly request the previous behavior (missing values instead of zeros) with the --mpt_mss flag (which stands for "empty missing").

   ncremap -P mpasseaice           --map=map.nc in.nc out.nc # Empty = 0.0
   ncremap -P mpasseaice --mpt_mss --map=map.nc in.nc out.nc # Empty = _FillValue

   http://nco.sf.net/nco.html#mpt_mss
2. ncremap supports new TempestRemap bilinear and integrated bilinear weight-generation algorithms. The algorithms sport the recommended names trbilin and trintbilin.

   ncremap --alg_typ=trbilin --grd_src=src.nc --grd_dst=dst.nc --map=map.nc
   ncremap --alg_typ=trintbilin --grd_src=src.nc --grd_dst=dst.nc --map=map.nc
   

   http://nco.sf.net/nco.html#tr
3. ncremap supports new "standard" names for E3SM v3 regridding algorithms and for older algorithms. These new names are simply synonyms for the existing algorithm names. No algorithm names have been deprecated (yet) so existing commands will still work. The new names are of the form ToolAlgorithm where Tool is esmf, nco, tr, or mbtr and Algorithm is the "classic" algorithm name, aave, bilin, etc.

   ncremap --alg_typ=esmfaave --grd_src=src.nc --grd_dst=dst.nc --map=map.nc
   ncremap --alg_typ=ncoaave  --grd_src=src.nc --grd_dst=dst.nc --map=map.nc
   ncremap --alg_typ=traave   --grd_src=src.nc --grd_dst=dst.nc --map=map.nc
   

   https://acme-climate.atlassian.net/wiki/spaces/DOC/pages/1217757434/Mapping+file+algorithms+and+naming+convention
4. ncks supports a new flag, --chk_xtn, that reports whether filename extensions comply with NASA's Dataset Interoperability Working Group (DIWG) which recommends ".nc", ".h5", and ".he5", depending on the API used to write the file. To check a file's compliance with the DIWG recommendation:

   ncks --chk_xtn ~/nco/data/in.nc
   ncks --chk_xtn ~/nco/data/in.nc4
   

   http://nco.sf.net/nco.htlm/chk_mss

Additional details are available in the ChangeLog.