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18 August 2017

Version 4.6.8 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:

Many new features in 4.6.8 are, as usual, related to climatologies and regridding. ncclimo can now be given an explicit list of seasons to compute instead of, or in addition to, MAM,JJA,SON,DJF. ncremap has improved mask and format handling. There are also a collection of minor bugfixes and improvements, including JSON tweaks, ISO8601 printing, and GCC7 and netCDF 4.5.x compatibility.

This release includes an important ncwa fix that prevents incorrect answers when hyperslabs are used with masks and/or weights. Upgrade if you use nc-d with -d hyperslabs.

PLEASE READ THIS IF YOU USE NCKS TO PRINT DATA:

The ncks default printing will change to CDL in summer 2017. For 20+ years ncks has, by default, dumped the text representation of a file in (what we call) "traditional" mode, which best facilitates meticulous data examination in line-by-line format. ncdump produces CDL format that is more useful for most NCO users. ncdump has always printed clean CDL and for many years there was little point in defaulting ncks printed output to CDL. However, ncks CDL mode now rivals ncdump in many ways. In particular, ncks --cln now prints times as human-readable calendar dates, the last ncdump feature that I used which ncks lacked. Hence in summer 2017 ncks default printed output will change to CDL. Then one will type simply "ncks" instead of "ncks --cdl". We just added a new "--trd" option to print traditional output. Use --trd in your scripts and their behavior will not change. Otherwise your printing scripts will start to print CDL this summer. You have been warned.

New Features

ncap2 now fully implements NCO chunking maps and policies. Previously ncap2 preserved existing chunking in variables, but could not be told to do anythin different. Now all command-line chunking behavior supported by NCO works in ncap2.
```
ncap2 --cnk_plc=unchunk -S cnk.nco in.nc4 out.nc4
```
http://nco.sf.net/nco.html#cnk
ncks CDL printing supports finer-grained control of date formats, including an ISO 8601 "T" option. Previously ncks printed UDUnits-compliant times as dates when invoked with the --cdl and --cal options. A third option, --dt_fmt, now exposes finer control of the format with short, regular, and ISO8601 options:
```
ncks -H -m -v time_bnds -C --cdl --dt_fmt=1 ~/nco/data/in.nc
ncks -H -m -v time_bnds -C --cdl --dt_fmt=2 ~/nco/data/in.nc
ncks -H -m -v time_bnds -C --cdl --dt_fmt=3 ~/nco/data/in.nc
dt_fmt:   Output:
0,1       1964-03-13 09:08:16 (Default, short format)
2         1964-03-13 09:08:16.000000 (regular format)
3         1964-03-13T09:08:16.000000 (ISO8601 "T" format)
```
Note that --dt_fmt automatically implies --cal.
http://nco.sf.net/nco.html#cln
Some data are best evaluated with custom-defined seasons, e.g., JFM instead of DJF, or two-month seasons such as FM or ON. ncclimo now supports up to eleven (and counting) seasons, although by default it only computes MAM, JJA, SON, and DJF. As of NCO 4.6.8, use the seasons option to specify additional or alternate seasons:
```
ncclimo --seasons=jfm,jas,ann -s 1980 -e 1983 -i drc_in -o drc_out
```
Use "–seasons=none" to completely turn-off seasonal and annual-mean climatologies:
```
ncclimo --seasons=none -s 1980 -e 1983 -i drc_in -o drc_out
```
http://nco.sf.net/nco.html#ncclimo
ncremap --msk_src and --msk_dst options now accept the value 'none' to prevent the regridder from interpreting any variable as a mask in files from which source or destination grids are inferred.
```
ncremap -i ~/ed.nc --msk_src=none -d ~/ed.nc -o ~/foo.nc
ncremap -i ~/ed.nc -d ~/ed.nc --msk_dst=none -o ~/foo.nc
```
http://nco.sf.net/nco.html#ncremap
ncremap now accepts standard NCO arguments for output file type. The -3, -4, -5, -6, and -7 flags, or their long-option equivalents --fl_fmt=fmt or --file_format=fmt where fmt is classic, netcdf4, 64bit_data, 64bit_offset, or netcdf4_classic (or some synonyms) causes the output files created by ncremap, e.g., the regridded files and the grid files, to have the requested format. The ERWG and TempestRemap weight-generators support only a subset of these formats.
```
ncremap -7 -i ~/deepthroat.nc -d ~/wapo.nc -o ~/foo.nc
```
http://nco.sf.net/nco.html#fl_fmt_ncremap