1NCES(1)                     General Commands Manual                    NCES(1)
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NAME

6       nces - netCDF Ensemble Statistics
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SYNTAX

9       nces  [-3]  [-4]  [-5]  [-6] [-7] [-A] [--bfr sz_byt][-C][-c][--cnk_byt
10       sz_byt][--cnk_csh   sz_byt][--cnk_dmn   nm,sz_lmn]   [--cnk_map    map]
11       [--cnk_min  sz_byt]  [--cnk_plc plc] [--cnk_scl sz_lmn][-D dbg_lvl] [-d
12       dim,[ min][,[ max]]] [--dbl|flt] [-F] [--fl_fmt=fmt] [-G  gpe_dsc]  [-g
13       grp[,...]]   [-h]  [--hdf]  [--hdr_pad  sz_byt]  [-L dfl_lvl] [-l path]
14       [--msa] [-N]  [-n  loop]  [--no_cll_msr]  [--no_frm_trm]  [--no_tmp_fl]
15       [--nsm_sfx  grp_sfx]  [-O]  [-p  path] [--ppc var1[, var2[,...]]= prc]]
16       [-R] [-r] [--ram_all] [-t thr_nbr] [--unn]  [-v  var[,...]]   [-X  box]
17       [-x] [-y op_typ] input-files output-file
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DESCRIPTION

20       nces  performs gridpoint averages of variables across an arbitrary num‐
21       ber (an ensemble) of input files, with each  file  receiving  an  equal
22       weight  in  the  average.  Each variable in the output-file will be the
23       same size as the same variable in any one of the  in  the  input-files,
24       and  all input-files must be the same size.  Whereas ncra only performs
25       averages over the record  dimension  (e.g.,  time),  and  weights  each
26       record  in the record dimension evenly, nces averages entire files, and
27       weights each file evenly.  All dimensions, including the record  dimen‐
28       sion, are treated identically and preserved in the output-file.
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30       The  file  is  the logical unit of organization for the results of many
31       scientific studies.  Often one wishes to generate a file which  is  the
32       gridpoint  average  of many separate files.  This may be to reduce sta‐
33       tistical noise by combining the results of a large  number  of  experi‐
34       ments,  or it may simply be a step in a procedure whose goal is to com‐
35       pute anomalies from a mean state.  In any case,  when  one  desires  to
36       generate  a  file whose properties are the mean of all the input files,
37       then nces is the operator to use.  nces assumes coordinate variable are
38       properties  common  to  all  of the experiments and so does not average
39       them across files.  Instead, nces copies the values of  the  coordinate
40       variables from the first input file to the output file.
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EXAMPLES

43       Consider  a  model  experiment which generated five realizations of one
44       year of data, say 1985.  You can imagine that the experimenter slightly
45       perturbs  the  initial conditions of the problem before generating each
46       new solution.  Assume each file contains all twelve months (a  seasonal
47       cycle)  of  data  and  we  want to produce a single file containing the
48       ensemble average (mean) seasonal cycle.  Here the numeric filename suf‐
49       fix denotes the experiment number (not the month):
50              nces 85_01.nc 85_02.nc 85_03.nc 85_04.nc 85_05.nc 85.nc
51              nces 85_0[1-5].nc 85.nc
52              nces -n 5,2,1 85_01.nc 85.nc
53       These  three  commands  produce  identical  answers.   The output file,
54       85.nc, is the same size as the inputs files.  It contains 12 months  of
55       data  (which  might  or  might  not  be stored in the record dimension,
56       depending on the input files), but each value in the output file is the
57       average of the five values in the input files.
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59       In  the  previous  example,  the  user could have obtained the ensemble
60       average values in a  particular  spatio-temporal  region  by  adding  a
61       hyperslab argument to the command, e.g.,
62              nces -d time,0,2 -d lat,-23.5,23.5 85_??.nc 85.nc
63       In this case the output file would contain only three slices of data in
64       the time dimension.  These three slices are the average  of  the  first
65       three  slices from the input files.  Additionally, only data inside the
66       tropics is included.
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68

AUTHOR

70       NCO manual pages written by Charlie Zender and originally formatted  by
71       Brian Mays.
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73

REPORTING BUGS

75       Report bugs to <http://sf.net/bugs/?group_id=3331>.
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79       Copyright © 1995-2018 Charlie Zender
80       This is free software; see the source for copying conditions.  There is
81       NO warranty; not even for MERCHANTABILITY or FITNESS FOR  A  PARTICULAR
82       PURPOSE.
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84

SEE ALSO

86       The full documentation for NCO is maintained as a Texinfo manual called
87       the NCO Users Guide.  Because NCO is mathematical in nature, the  docu‐
88       mentation  includes  TeX-intensive  portions not viewable on character-
89       based displays.  Hence the only complete and authoritative versions  of
90       the NCO Users Guide are the PDF (recommended), DVI, and Postscript ver‐
91       sions at <http://nco.sf.net/nco.pdf>, <http://nco.sf.net/nco.dvi>,  and
92       <http://nco.sf.net/nco.ps>,  respectively.   HTML  and XML versions are
93       available         at          <http://nco.sf.net/nco.html>          and
94       <http://nco.sf.net/nco.xml>, respectively.
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96       If  the  info and NCO programs are properly installed at your site, the
97       command
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99              info nco
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101       should give you access to the complete  manual,  except  for  the  TeX-
102       intensive portions.
103
104       ncap(1), ncap2(1), ncatted(1), ncbo(1), ncclimo(1), nces(1), ncecat(1),
105       ncflint(1), ncks(1), nco(1), ncpdq(1), ncra(1), ncrcat(1),  ncremap(1),
106       ncrename(1), ncwa(1)
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HOMEPAGE

110       The NCO homepage at <http://nco.sf.net> contains more information.
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