1NCWA(1) General Commands Manual NCWA(1)
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6 ncwa - netCDF Weighted Averager
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9 ncwa [-3] [-4] [-5] [-6] [-7] [-A] [-a dim[,...]] [-B mask_cond] [-b]
10 [--bfr sz_byt][-C][-c] [--cmp cmp_sng] [--cnk_byt sz_byt][--cnk_csh
11 sz_byt][--cnk_dmn nm,sz_lmn] [--cnk_map map] [--cnk_min sz_byt]
12 [--cnk_plc plc] [--cnk_scl sz_lmn][-D dbg_lvl] [-d dim,[ min][,[ max]]]
13 [--dbl|flt] [-F] [--fl_fmt=fmt] [-G gpe_dsc] [-g grp[,...]] [--glb
14 att_name= att_val]] [-h] [--hdf] [--hdr_pad sz_byt][--hpss_try] [-I]
15 [-L dfl_lvl][-l path] [-M val] [-m mask] [-N] [--no_cll_msr]
16 [--no_cll_mth] [--no_frm_trm] [--no_tmp_fl] [-O] [-o output-file] [-p
17 path] [--ppc var1[, var2[,...]]= prc]] [-R] [-r] [--ram_all] [-T
18 mask_comp] [-t thr_nbr] [--uio] [--unn] [-v var[,...]] [-w weight]
19 [-x] [-y op_typ] input-file output-file
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22 ncwa averages variables in a single file over arbitrary dimensions,
23 with options to specify weights, masks, and normalization. The default
24 behavior of ncwa is to arithmetically average every numerical variable
25 over all dimensions and produce a scalar result. To average variables
26 over only a subset of their dimensions, specify these dimensions in a
27 comma-separated list following -a, e.g., -a time,lat,lon. As with all
28 arithmetic operators, the operation may be restricted to an arbitrary
29 hypserslab by employing the -d option ncwa also handles values matching
30 the variable's _FillValue attribute correctly. Moreover, ncwa under‐
31 stands how to manipulate user-specified weights, masks, and normaliza‐
32 tion options. With these options, ncwa can compute sophisticated aver‐
33 ages (and integrals) from the command line.
34 mask and weight, if specified, are broadcast to conform to the vari‐
36 ables being averaged. The rank of variables is reduced by the number
37 of dimensions which they are averaged over. Thus arrays which are one
38 dimensional in the input-file and are averaged by ncwa appear in the
39 output-file as scalars. This allows the user to infer which dimensions
40 may have been averaged. Note that that it is impossible for ncwa to
41 make make a weight or mask of rank W conform to a var of rank V if W >
42 V. This situation often arises when coordinate variables (which, by
43 definition, are one dimensional) are weighted and averaged. ncwa as‐
44 sumes you know this is impossible and so ncwa does not attempt to
45 broadcast weight or mask to conform to var in this case, nor does ncwa
46 print a warning message telling you this, because it is so common.
47 Specifying dbg > 2 does cause ncwa to emit warnings in these situa‐
48 tions, however.
49 Non-coordinate variables are always masked and weighted if specified.
51 Coordinate variables, however, may be treated specially. By default,
52 an averaged coordinate variable, e.g., latitude, appears in output-file
53 averaged the same way as any other variable containing an averaged di‐
54 mension. In other words, by default ncwa weights and masks coordinate
55 variables like all other variables. This design decision was intended
56 to be helpful but for some applications it may be preferable not to
57 weight or mask coordinate variables just like all other variables.
58 Consider the following arguments to ncwa: “-a latitude -w lat_wgt -d
59 latitude,0.,90.” where lat_wgt is a weight in the latitude dimension.
60 Since, by default ncwa weights coordinate variables, the value of lati‐
61 tude in the output-file depends on the weights in lat_wgt and is not
62 likely to be 45.---the midpoint latitude of the hyperslab. Option -I
63 overrides this default behavior and causes ncwa not to weight or mask
64 coordinate variables. In the above case, this causes the value of lat‐
65 itude in the output-file to be 45.---which is a somewhat appealing re‐
66 sult. Thus, -I specifies simple arithmetic averages for the coordinate
67 variables. In the case of latitude, -I specifies that you prefer to
68 archive the central latitude of the hyperslab over which variables were
69 averaged rather than the area weighted centroid of the hyperslab. Note
70 that the default behavior of ( -I) changed on 1998/12/01---before this
71 date the default was not to weight or mask coordinate variables. The
72 mathematical definition of operations involving rank reduction is given
73 above.
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77 NCO manual pages written by Charlie Zender and originally formatted by
78 Brian Mays.
79
82 Report bugs to <http://sf.net/bugs/?group_id=3331>.
83
86 Copyright © 1995-present Charlie Zender
87 This is free software; see the source for copying conditions. There is
88 NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
89 PURPOSE.
90
93 The full documentation for NCO is maintained as a Texinfo manual called
94 the NCO Users Guide. Because NCO is mathematical in nature, the docu‐
95 mentation includes TeX-intensive portions not viewable on character-
96 based displays. Hence the only complete and authoritative versions of
97 the NCO Users Guide are the PDF (recommended), DVI, and Postscript ver‐
98 sions at <http://nco.sf.net/nco.pdf>, <http://nco.sf.net/nco.dvi>, and
99 <http://nco.sf.net/nco.ps>, respectively. HTML and XML versions are
100 available at <http://nco.sf.net/nco.html> and
101 <http://nco.sf.net/nco.xml>, respectively.
102 If the info and NCO programs are properly installed at your site, the
104 command
105 info nco
107 should give you access to the complete manual, except for the TeX-in‐
109 tensive portions.
110 ncap(1), ncap2(1), ncatted(1), ncbo(1), ncclimo(1), nces(1), ncecat(1),
112 ncflint(1), ncks(1), nco(1), ncpdq(1), ncra(1), ncrcat(1), ncremap(1),
113 ncrename(1), ncwa(1)
114
117 The NCO homepage at <http://nco.sf.net> contains more information.
118 NCWA(1)