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Version 4.8.1 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 4.8.1 primarily contains enhancements to the vertical interpolation feature of ncremap, ncclimo, and ncks. Two extrapolation options are now supported (nearest neighbor and missing value), and the entire procedure now works with the ECMWF IFS hybrid sigma pressure grid as input. Other changes include better support for north-to-south (n2s) Gaussian grid inferral and output, and ncclimo updates and improvements for finer-grained MPI parallelism.

New Features

1. ncremap/ncks now always creates/infers north-to-south grids with polygons in counter-clockwise (CCW) orientation. Formerly, polygons in south-to-north grids had CCW orientation while those in north-to-south grids had CW orientation.

   ncremap -G latlon=1280,2560#lat_typ=gss#lat_drc=n2s -g $HOME/grd_n2s.nc
   ncremap -d ecmwf_ifs.nc -g grd_n2s.nc

   http://nco.sf.net/nco.html#n2s
   http://nco.sf.net/nco.html#ncremap
2. ncremap now vertically interpolates data from ECMWF IFS hybrid vertical grid format to CAM/E3SM hybrid format and to pure-pressure format. ECMWF archives and serves IFS data in a hybrid sigma-pressure grid format significantly different from CAM/E3SM. ECMWF supplies lnsp (log surface pressure) not PS (surface pressure). There are numerous other metadata differences. NCO now automatically takes care of these.

   ncremap --vrt=vrt_hyb_L72.nc ecmwf_ifs_f640L137.nc out.nc

   http://nco.sf.net/nco.html#vrt_fl
   http://nco.sf.net/nco.html#ncremap
3. ncks, ncremap, and ncclimo now support two different extrapolation algorithms for vertical regridding. The original and default extrapolation algorithm uses the nearest valid neighbor. This is now explicitly selectable with --vrt_xtr=nrs_ngh. The second supported algorithm extrapolates to missing values. This is now explicitly selectable with --vrt_xtr=mss_val.

   ncremap --vrt=vrt.nc --vrt_xtr=mss_val in.nc out.nc
   ncremap --vrt=vrt.nc --vrt_xtr=nrg_ngh in.nc out.nc
   ncclimo --vrt=vrt.nc --vrt_xtr=mss_val -i drc_raw -O drc_rgr
   ncks --vrt=vrt.nc --rgr vrt_xtr=mss_val in.nc out.nc

   http://nco.sf.net/nco.html#vrt_xtr
   http://nco.sf.net/nco.html#ncremap
4. The former ncremap ESMF extrapolation options xtr_nsp, xtr_typ, and xtr_xpn have been renamed esmf_nsp, esmf_typ, and esmf_xpn, respectively. This was done to make them easier to find and to segregate regridder-specific from regridder-generic options.
   http://nco.sf.net/nco.html#esmf_typ
   http://nco.sf.net/nco.html#ncremap
5. ncremap accepts a new option, --msh_fl=msh.nc, to specify the name of the intersection mesh-file. This option only works with the TempestRemap and NCO weight-generators. (The NCO weight-generator is still in development and is not yet supported. Interested beta testers can access it with --alg_typ=nco).
6. ncremap MWF mode now only generates TempestRemap maps when one or both input grids are Exodus-format (and end with a .g suffix). This was done to keep ERWG and TR map-generation from being interdependent in case a grid-pair breaks one or the other.

Additional details are available in the ChangeLog.