NCO User’s Guide
A suite of netCDF operators
Edition 4.3.5, for NCO Version 4.3.5
August 2013
by Charlie Zender
Department of Earth System Science
University of California, Irvine
Copyright
c
1995–2013 Charlie Zender.
This is the first edition of the NCO User’s Guide,
and is consistent with version 2 of ‘texinfo.tex’.
Published by Charlie Zender
Department of Earth System Science
3200 Croul Hall
University of California, Irvine
Irvine, CA 92697-3100 USA
Permission is granted to copy, distribute and/or modify this document under the terms of
the GNU Free Documentation License, Version 1.3 or any later version published by the Free
Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. The license is available online at http://www.gnu.org/copyleft/fdl.html
The original author of this software, Charlie Zender, wants to improve it with the help of
your suggestions, improvements, bug-reports, and patches.
Charlie Zender <surname at uci dot edu> (yes, my surname is zender)
Department of Earth System Science
3200 Croul Hall
University of California, Irvine
Irvine, CA 92697-3100
Foreword 1
Foreword
NCO is the result of software needs that arose while I worked on projects funded by NCAR,
NASA, and ARM. Thinking they might prove useful as tools or templates to others, it
is my pleasure to provide them freely to the scientific community. Many users (most of
whom I have never met) have encouraged the development of NCO. Thanks espcially to Jan
Polcher, Keith Lindsay, Arlindo da Silva, John Sheldon, and William Weibel for stimulating
suggestions and correspondence. Your encouragment motivated me to complete the NCO
User’s Guide. So if you like NCO, send me a note! I should mention that NCO is not
connected to or officially endorsed by Unidata, ACD, ASP, CGD, or Nike.
Charlie Zender
May 1997
Boulder, Colorado
Major feature improvements entitle me to write another Foreword. In the last five years
a lot of work has been done to refine NCO. NCO is now an open source project and appears
to be much healthier for it. The list of illustrious institutions that do not endorse NCO
continues to grow, and now includes UCI.
Charlie Zender
October 2000
Irvine, California
The most remarkable advances in NCO capabilities in the last few years are due to con-
tributions from the Open Source community. Especially noteworthy are the contributions
of Henry Butowsky and Rorik Peterson.
Charlie Zender
January 2003
Irvine, California
NCO was generously supported from 2004–2008 by US National Science Foundation
(NSF) grant IIS-0431203. This support allowed me to maintain and extend core NCO code,
and others to advance NCO in new directions: Gayathri Venkitachalam helped implement
2 NCO 4.3.5 User’s Guide
MPI; Harry Mangalam improved regression testing and benchmarking; Daniel Wang de-
veloped the server-side capability, SWAMP; and Henry Butowsky, a long-time contributor,
developed ncap2. This support also led NCO to debut in professional journals and meetings.
The personal and professional contacts made during this evolution have been immensely
rewarding.
Charlie Zender
March 2008
Grenoble, France
The end of the NSF SEI grant in August, 2008 curtailed NCO development. Fortunately
we could justify supporting Henry Butowsky on other research grants until May, 2010 while
he developed the key ncap2 features used in our climate research. And recentely the NASA
ACCESS program commenced funding NCO support for netCDF4 group functionality.
Thus NCO will grow and evade bit-rot for the foreseeable future.
On a personal level, I continue to receive with gratitude the thanks of NCO users at
nearly every scientific meeting I attend. People introduce themselves, shake my hand and
extol, sometimes rather effusively, these time-saving tools. These exchanges lighten me like
anti-gravity. Sometimes I daydream how many hours NCO has turned from grunt work to
productive research, or from research into early happy hours. It’s a cool feeling.
Charlie Zender
2012
Irvine, California
Summary 3
Summary
This manual describes NCO, which stands for netCDF Operators. NCO is a suite of programs
known as operators. Each operator is a standalone, command line program executed at
the shell-level like, e.g., ls or mkdir. The operators take netCDF files (including HDF5
files constructed using the netCDF API) as input, perform an operation (e.g., averaging or
hyperslabbing), and produce a netCDF file as output. The operators are primarily designed
to aid manipulation and analysis of data. The examples in this documentation are typical
applications of the operators for processing climate model output. This stems from their
origin, though the operators are as general as netCDF itself.
