Provided by: nco_4.5.4-1build1_amd64 
NAME
ncwa - netCDF Weighted Averager
SYNTAX
ncwa [-3] [-4] [-6] [-7] [-A] [-a dim[,...]] [-B mask_cond] [-b] [--bfr sz][-C][-c][--cnk_byt
sz][--cnk_dmn nm,sz] [--cnk_map map] [--cnk_min sz] [--cnk_plc plc] [--cnk_scl sz][-D dbg_lvl] [-d dim,[
min][,[ max]]] [--dbl|flt] [-F] [-G gpe_dsc] [-g grp[,...]] [--glb att_name= att_val]] [-h] [--hdf]
[--hdr_pad sz] [-I] [-L dfl_lvl][-l path] [-M val] [-m mask] [-N] [--no_cll_mth] [--no_tmp_fl] [-O] [-o
output-file] [-p path] [--ppc var1[, var2[,...]]= prc]] [-R] [-r] [--ram_all] [-T mask_comp] [-t thr_nbr]
[--unn] [-v var[,...]] [-w weight] [-x] [-y op_typ] input-file output-file
DESCRIPTION
ncwa averages variables in a single file over arbitrary dimensions, with options to specify weights,
masks, and normalization. The default behavior of ncwa is to arithmetically average every numerical
variable over all dimensions and produce a scalar result. To average variables over only a subset of
their dimensions, specify these dimensions in a comma-separated list following -a, e.g., -a time,lat,lon.
As with all arithmetic operators, the operation may be restricted to an arbitrary hypserslab by employing
the -d option ncwa also handles values matching the variable's _FillValue attribute correctly. Moreover,
ncwa understands how to manipulate user-specified weights, masks, and normalization options. With these
options, ncwa can compute sophisticated averages (and integrals) from the command line.
mask and weight, if specified, are broadcast to conform to the variables being averaged. The rank of
variables is reduced by the number of dimensions which they are averaged over. Thus arrays which are one
dimensional in the input-file and are averaged by ncwa appear in the output-file as scalars. This allows
the user to infer which dimensions may have been averaged. Note that that it is impossible for ncwa to
make make a weight or mask of rank W conform to a var of rank V if W > V. This situation often arises
when coordinate variables (which, by definition, are one dimensional) are weighted and averaged. ncwa
assumes you know this is impossible and so ncwa does not attempt to broadcast weight or mask to conform
to var in this case, nor does ncwa print a warning message telling you this, because it is so common.
Specifying dbg > 2 does cause ncwa to emit warnings in these situations, however.
Non-coordinate variables are always masked and weighted if specified. Coordinate variables, however, may
be treated specially. By default, an averaged coordinate variable, e.g., latitude, appears in output-
file averaged the same way as any other variable containing an averaged dimension. In other words, by
default ncwa weights and masks coordinate variables like all other variables. This design decision was
intended to be helpful but for some applications it may be preferable not to weight or mask coordinate
variables just like all other variables. Consider the following arguments to ncwa: “-a latitude -w
lat_wgt -d latitude,0.,90.” where lat_wgt is a weight in the latitude dimension. Since, by default ncwa
weights coordinate variables, the value of latitude in the output-file depends on the weights in lat_wgt
and is not likely to be 45.---the midpoint latitude of the hyperslab. Option -I overrides this default
behavior and causes ncwa not to weight or mask coordinate variables. In the above case, this causes the
value of latitude in the output-file to be 45.---which is a somewhat appealing result. Thus, -I
specifies simple arithmetic averages for the coordinate variables. In the case of latitude, -I specifies
that you prefer to archive the central latitude of the hyperslab over which variables were averaged
rather than the area weighted centroid of the hyperslab. Note that the default behavior of ( -I) changed
on 1998/12/01---before this date the default was not to weight or mask coordinate variables. The
mathematical definition of operations involving rank reduction is given above.
AUTHOR
NCO manual pages written by Charlie Zender and originally formatted by Brian Mays.
REPORTING BUGS
Report bugs to <http://sf.net/bugs/?group_id=3331>.
COPYRIGHT
Copyright © 1995-2016 Charlie Zender
This is free software; see the source for copying conditions. There is NO warranty; not even for
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
The full documentation for NCO is maintained as a Texinfo manual called the NCO User's Guide. Because
NCO is mathematical in nature, the documentation includes TeX-intensive portions not viewable on
character-based displays. Hence the only complete and authoritative versions of the NCO User's Guide are
the PDF (recommended), DVI, and Postscript versions at <http://nco.sf.net/nco.pdf>,
<http://nco.sf.net/nco.dvi>, and <http://nco.sf.net/nco.ps>, respectively. HTML and XML versions are
available at <http://nco.sf.net/nco.html> and <http://nco.sf.net/nco.xml>, respectively.
If the info and NCO programs are properly installed at your site, the command
info nco
should give you access to the complete manual, except for the TeX-intensive portions.
ncap(1), ncap2(1), ncatted(1), ncbo(1), nces(1), ncecat(1), ncflint(1), ncks(1), nco(1), ncpdq(1),
ncra(1), ncrcat(1), ncremap(1), ncrename(1), ncwa(1)
HOMEPAGE
The NCO homepage at <http://nco.sf.net> contains more information.
NCWA(1)