« EarthCube Program... | Main | 2017 DeSouza Award... »

Version 4.6.4 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:

The main new features in 4.6.4 are the "splitter" and daily climatology capabilities for ncclimo. ncclimo now generates, combines existing, and splits climatologies. Thus it is a fairly general purpose climatology operator. NCO now supports two more CF conventions (formula_terms and cell_measures), and has a few bugfixes.

New Features

1. ncclimo will reshape timeseries, i.e., split input datasets into per-variable files that span the entire timeseries. Input files are specified via stdin, via positional arguments (after all options) on the command-line, or as the set of .nc files in drc_in

   ls $drc_in/*.nc | ncclimo -v T,Q --output=drc_out --map=rgr_map
   ncclimo -v T,Q --output=drc_out --map=rgr_map < list
   ncclimo -v T,Q --output=drc_out --map=rgr_map $drc_in/*.nc
   ncclimo -v T,Q --input=$drc_in --output=drc_out --map=rgr_map

   http://nco.sf.net/nco.html#ncclimo
2. ncks allows setting per-variable chunk cache-size with --cnk_csh. The effects of varying chunk cache-size are not well understood, at least by we who work on NCO. Users asked for a knob to tune it, and now that exists. Experiment with this and if you find reasons for NCO to set this to non-default values, let us know. If you want more knobs, let us know. This setting only works on netCDF4 files.

   ncks -D 3 --cnk_csh 1000000 in.nc4 out.nc

   http://nco.sf.net/nco.html#cnk_csh
3. ncremap now includes staggered grid weights with FV grid output. The weights are named w_stag, following the CESM CAM convention.
   http://nco.sf.net/nco.html#ncremap
4. Variables listed in a formula_terms attribute are now extracted by default. Turn-off this behavior with --no_frm_trm. The CF formula_terms convention is used to associate variables with terms in defined formulas, such as vertical coordinates:
   lev:standard_name = "atmosphere_hybrid_sigma_pressure_coordinate"
lev:formula_terms = "a: hyam b: hybm p0: P0 ps: PS"
   Unless the default behavior is overridden, NCO attaches any formula variables to the extraction list along with the primary variable and other associated variables. By definition, formula variables are a subset of the rank of the variable they define.
   http://nco.sf.net/nco.html#frm_trm
5. Variables listed in a cell_measures attribute are now extracted by default. Turn-off this behavior with --no_cll_msr. This convention allows variables to indicate which other variables contains area or volume information about a gridcell. These measures variables are pointed to by the cell_measures attribute. Unless the default behavior is overridden, NCO attaches all measures variables to the extraction list along with the primary variable.
   http://nco.sf.net/nco.html#cll_msr

Additional details are available in the ChangeLog.