1NCEA(1)                     General Commands Manual                    NCEA(1)
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NAME

6       ncea - netCDF Ensemble Averager
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SYNTAX

9       ncea  [-3]  [-4]  [-6] [-A] [-C] [-c] [-D dbg] [-d dim,[ min][,[ max]]]
10       [-F] [-h] [-L dfl_lvl] [-l path] [-n loop] [-O] [-p path] [-R] [-r] [-t
11       thr_nbr]  [-v var[,...]]  [-X box] [-x] [-y op_typ] input-files output-
12       file
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DESCRIPTION

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

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

65       NCO manual pages written by Charlie Zender and Brian Mays.
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REPORTING BUGS

69       Report bugs to <http://sf.net/bugs/?group_id=3331>.
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73       Copyright © 1995-2010 Charlie Zender
74       This is free software; see the source for copying conditions.  There is
75       NO warranty; not even for MERCHANTABILITY or FITNESS FOR  A  PARTICULAR
76       PURPOSE.
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SEE ALSO

80       The full documentation for NCO is maintained as a Texinfo manual called
81       the NCO User's Guide.  Because NCO is mathematical in nature, the docu‐
82       mentation  includes  TeX-intensive  portions not viewable on character-
83       based displays.  Hence the only complete and authoritative versions  of
84       the  NCO  User's  Guide  are the PDF (recommended), DVI, and Postscript
85       versions at  <http://nco.sf.net/nco.pdf>,  <http://nco.sf.net/nco.dvi>,
86       and  <http://nco.sf.net/nco.ps>,  respectively.   HTML and XML versions
87       are      available      at       <http://nco.sf.net/nco.html>       and
88       <http://nco.sf.net/nco.xml>, respectively.
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90       If  the  info and NCO programs are properly installed at your site, the
91       command
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93              info nco
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95       should give you access to the complete  manual,  except  for  the  TeX-
96       intensive portions.
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HOMEPAGE

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