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Version 5.1.5 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 5.1.5 polishes the new vertical interpolation capabilities introduced in 5.1.3 and 5.1.4, improves the safety NCZarr operations, and fixes minor ncremap bugs. This release can be skipped if these regridding and NCZarr features are not useful to you.

New Features

1. ncremap now behaves more sensibly when vertically interpolating MPAS-Ocean files/fields. Previously, users had to explicitly add the multidimensional auxiliary depth coordinate (often timeMonthly_avg_zMid) to the subsetted list of variables whenever the subset list option (-v var1,var2...) was used. This is because most MPAS datasets do not adhere to the CF "coordinates" convention, and NCO has no way of knowing which auxiliary coordinates contain the depth field. Now ncremap uses the -P mpasocean option to trigger a search for the zMid coordinate in the input file. If found, ncremap automatically adds it to the subset as appropriate.

   ncremap -P mpas --vrt_out=vrt.nc --map=map.nc in.nc out.nc

   http://nco.sf.net/nco.html#ncremap
   http://nco.sf.net/nco.html#vrt_out
2. ncremap has a --ps_rtn (--retain_surface_pressure) switch to facilitate "round-trip" vertical interpolation such as hybrid->pressure->hybrid. By default ncremap excludes the surface pressure field from the output after hybrid->pressure interpolation. The --ps_rtn switch (which takes no argument) instructs the regridder to retain the surface pressure field after hybrid->pressure interpolation. This field is then available for subsequent interpolation back to a hybrid vertical coordinate.

   ncremap --ps_rtn --ps_nm=ps --vrt_out=ncep.nc in.nc out_ncep.nc
   ncremap --ps_rtn -v T,Q,U,PS --vrt_out=ncep.nc in.nc out_ncep.nc
   ncremap --vrt_out=hybrid.nc out_ncep.nc out_hybrid.nc
   

   http://nco.sf.net/nco.html#ps_rtn
3. NCO is now more careful about overwriting existing directories and files with NCZarr stores. Previously NCO would overwrite any directory or file that the netCDF library could successfully open. However, netCDF library versions 4.8.0->4.9.1 "succeed" in opening non-NCZarr stores. Hence additional precautions are necessary to avoid unintentionally overwriting non-NCZarr paths with NCZarr stores. For example,

   ncks in_zarr4.nc file://${HOME}/ncz_dnd/foo#mode=nczarr,file

   now overwrites "foo" only if it is already an NCZarr store. Previously foo would be overwritten if it already existed yet was not a valid NCZarr store.
4. NCO improves handling of output from the DOE EAMxx model in two ways. First, NCO now treats this model output as CF-compliant. This causes NCO to implement special conventions such as carrying multi-dimensional auxiliary coordinate variables when subsetting. Second, ncremap automatically permutes EAMxx datasets that have been interpolated to pressure levels to have the correct dimension ordering (horizontal dimension as most-rapidly-varying) prior to horizontal regridding.

Additional details are available in the ChangeLog.