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

6       ncea - netCDF Ensemble Averager
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SYNTAX

9       ncea  [-A]  [-C]  [-c]  [-D dbg] [-d dim,[ min][,[ max]]] [-F] [-h] [-l
10       path] [-n loop] [-O] [-p path]  [-R]  [-r]  [-v  var[,...]]   [-x]  [-y
11       op_typ] input-files output-file
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DESCRIPTION

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

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

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

68       Report bugs to <http://sf.net/bugs/?group_id=3331>.
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72       Copyright © 1995-2004 Charlie Zender
73       This is free software; see the source for copying conditions.  There is
74       NO  warranty;  not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
75       PURPOSE.
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SEE ALSO

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

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