NAME

       nces - netCDF Ensemble Statistics

SYNTAX

       nces  [-3]  [-4]  [-6]  [-7]  [-A]  [--bfr  sz][-C][-c][--cnk_byt  sz][--cnk_dmn  nm,sz]  [--cnk_map map]
       [--cnk_plc plc] [--cnk_scl sz][-D dbg_lvl] [-d dim,[ min][,[ max]]] [--dbl|flt]  [-F]  [-G  gpe_dsc]  [-g
       grp[,...]]  [-h] [--hdf] [--hdr_pad sz] [-L dfl_lvl] [-l path] [--msa] [-n loop] [--no_tmp_fl] [--nsm_sfx
       grp_sfx] [-O] [-p path] [-R] [-r] [--ram_all] [-t thr_nbr] [--unn] [-v  var[,...]]   [-X  box]  [-x]  [-y
       op_typ] input-files output-file

DESCRIPTION

       nces  performs  gridpoint  averages of variables across an arbitrary number (an ensemble) of input files,
       with each file receiving an equal weight in the average.  Each variable in the output-file  will  be  the
       same size as the same variable in any one of the in the input-files, and all input-files must be the same
       size.  Whereas ncra only performs averages over the record  dimension  (e.g.,  time),  and  weights  each
       record  in  the  record  dimension evenly, nces averages entire files, and weights each file evenly.  All
       dimensions, including the record dimension, are treated identically and preserved in the output-file.

       The file is the logical unit of organization for the results  of  many  scientific  studies.   Often  one
       wishes  to  generate a file which is the gridpoint average of many separate files.  This may be to reduce
       statistical noise by combining the results of a large number of experiments, or it may simply be  a  step
       in  a  procedure  whose goal is to compute anomalies from a mean state.  In any case, when one desires to
       generate a file whose properties are the mean of all the input files, then nces is the operator  to  use.
       nces  assumes coordinate variable are properties common to all of the experiments and so does not average
       them across files.  Instead, nces copies the values of the coordinate variables from the first input file
       to the output file.

EXAMPLES

       Consider  a  model  experiment  which generated five realizations of one year of data, say 1985.  You can
       imagine that the experimenter slightly perturbs the initial conditions of the problem  before  generating
       each new solution.  Assume each file contains all twelve months (a seasonal cycle) of data and we want to
       produce a single file containing the ensemble average (mean) seasonal cycle.  Here the  numeric  filename
       suffix denotes the experiment number (not the month):
              nces 85_01.nc 85_02.nc 85_03.nc 85_04.nc 85_05.nc 85.nc
              nces 85_0[1-5].nc 85.nc
              nces -n 5,2,1 85_01.nc 85.nc
       These  three  commands produce identical answers.  The output file, 85.nc, is the same size as the inputs
       files.  It contains 12 months of data (which might or might  not  be  stored  in  the  record  dimension,
       depending on the input files), but each value in the output file is the average of the five values in the
       input files.

       In the previous example, the user could have obtained the ensemble average values in a particular spatio-
       temporal region by adding a hyperslab argument to the command, e.g.,
              nces -d time,0,2 -d lat,-23.5,23.5 85_??.nc 85.nc
       In  this case the output file would contain only three slices of data in the time dimension.  These three
       slices are the average of the first three slices from the input files.  Additionally,  only  data  inside
       the tropics is included.

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 © 1995-2010 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.

HOMEPAGE

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

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