NCEA(1) 						      General Commands Manual							   NCEA(1)

NAME

       ncea - netCDF Ensemble Averager

SYNTAX

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

DESCRIPTION

       ncea 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, ncea 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 experi-
       ments, 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 ncea is the operator to use.  ncea assumes coordinate variable
       are properties common to all of the experiments and so does not average them across files.  Instead, ncea copies the values of the  coordi-
       nate 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):
	      ncea 85_01.nc 85_02.nc 85_03.nc 85_04.nc 85_05.nc 85.nc
	      ncea 85_0[1-5].nc 85.nc
	      ncea -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 hyper-
       slab argument to the command, e.g.,
	      ncea -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 Brian Mays.

REPORTING BUGS

       Report bugs to <http://sf.net/bugs/?group_id=3331>.

COPYRIGHT

       Copyright (C) 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 PARTICU-
       LAR 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.

																	   NCEA(1)