ncra - Man Page

netCDF Record Averager


ncra [-3] [-4] [-5] [-6] [-7] [-A] [--bfr sz_byt] [-C] [-c] [--cb y1,y2,m1,m2,tpd] [--cmp cmp_sng] [--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]][, stride[[,[ subcycle[[,[ interleave]]]]]] [--dbl|flt] [-F] [--fl_fmt=fmt] [-G gpe_dsc] [-g   grp[,...]] [--glb att_name= att_val]] [-H] [-h] [--hdf] [--hdr_pad sz_byt] [--hpss_try] [-L dfl_lvl] [-l path] [--mro] [--msa] [-N] [-n loop] [--no_cll_msr] [--no_cll_mth] [--no_frm_trm] [--no_tmp_fl] [-O] [-p path] [--ppc var1[, var2[,...]]= prc]] [--prm_int] [--prw wgt_arr] [-R] [-r] [--ram_all] [--rec_apn] [-t thr_nbr] [--uio] [--unn] [-v var[,...]] [-w wgt] [-X box] [-x] [-y op_typ] input-files output-file


ncra averages record variables across an arbitrary number of input files. The record dimension is retained as a degenerate (size 1) dimension in the output variables.

Input files may vary in size, but each must have a record dimension. The record coordinate, if any, should be monotonic for (or else non-fatal warnings may be generated). Hyperslabs of the record dimension which include more than one file are handled correctly. ncra supports the stride argument to the -d hyperslab option for the record dimension only, stride is not supported for non-record dimensions.

ncra weights each record (e.g., time slice) in the input-files equally. ncra does not attempt to see if, say, the time coordinate is irregularly spaced and thus would require a weighted average in order to be a true time average.


Average files,,  ... along the record dimension, and store the results in

ncra 8[56789].nc
ncra -n 5,2,1

These three methods produce identical answers.

Assume the files,,  ... each contain a record coordinate time of length 12 defined such that the third record in contains data from March 1986, etc. NCO knows how to hyperslab the record dimension across files. Thus, to average data from December, 1985 through February, 1986:

ncra -d time,11,13
ncra -F -d time,12,14

The file is superfluous, but does not cause an error. The -F turns on the Fortran (1-based) indexing convention. The following uses the stride option to average all the March temperature data from multiple input files into a single output file

ncra -F -d time,3,,12 -v temperature

Assume the time coordinate is incrementally numbered such that January, 1985 = 1 and December, 1989 = 60. Assuming ?? only expands to the five desired files, the following averages June, 1985--June, 1989:

ncra -d time,6.,54. ??.nc


NCO manual pages written by Charlie Zender and originally formatted by Brian Mays.

Reporting Bugs

Report bugs to <>.

See Also

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 <>, <>, and <>, respectively. HTML and XML versions are available at <> and <>, 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.

ncap2(1), ncatted(1), ncbo(1), ncclimo(1), nces(1), ncecat(1), ncflint(1), ncz2psx(1), ncks(1), nco(1), ncpdq(1), ncra(1), ncrcat(1), ncremap(1), ncrename(1), ncwa(1)


The NCO homepage at <> contains more information.

Referenced By

ncap2(1), ncatted(1), ncclimo(1), ncecat(1), nces(1), ncflint(1), ncks(1), nco(1), ncpdq(1), ncrcat(1), ncremap(1), ncrename(1), ncwa(1), ncz2psx(1).