Ubuntu Manpage: nces - netCDF Ensemble Statistics

NAME

       nces - netCDF Ensemble Statistics

SYNTAX

       nces  [-3]  [-4]  [-5]  [-6]  [-7]  [-A]  [--bfr  sz_byt] [-C] [-c] [--cb y1,y2,m1,m2,tpd]
       [--cnk_byt sz_byt] [--cnk_csh sz_byt] [--cnk_dmn  nm,sz_lmn]  [--cnk_map  map]  [--cnk_min
       sz_byt]  [--cnk_plc  plc]  [--cnk_scl  sz_lmn]  [-D  dbg_lvl]  [-d  dim,[  min][,[  max]]]
       [--dbl|flt] [-F] [--fl_fmt=fmt] [-G  gpe_dsc]  [-g  grp[,...]]   [-h]  [--hdf]  [--hdr_pad
       sz_byt]  [-L  dfl_lvl]  [-l  path]  [--msa]  [-N]  [-n loop] [--no_cll_msr] [--no_frm_trm]
       [--no_tmp_fl] [--nsm_sfx grp_sfx] [-O] [-p path] [--ppc  var1[,  var2[,...]]=  prc]]  [-R]
       [-r]  [--ram_all]  [-t  thr_nbr] [--uio] [--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-present 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.

       The full documentation for NCO is maintained as a Texinfo  manual  called  the  NCO  Users
       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  Users  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.

       ncap(1),  ncap2(1),  ncatted(1),  ncbo(1),  ncclimo(1),  nces(1),  ncecat(1),  ncflint(1),
       ncks(1), nco(1), ncpdq(1), ncra(1), ncrcat(1), ncremap(1), ncrename(1), ncwa(1)

HOMEPAGE

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

                                                                                          NCES(1)