ncra - Online in the Cloud

PROGRAM:

NAME

ncra - netCDF Record Averager

SYNTAX

ncra [-3] [-4] [-6] [-7] [-A] [--bfr sz][-C][-c][--cnk_byt sz][--cnk_dmn nm,sz] [--cnk_map
map] [--cnk_min sz] [--cnk_plc plc] [--cnk_scl sz][-D dbg_lvl] [-d dim,[ min][,[ max]][,
stride[[,[ subcycle]]]]] [--dbl|flt] [-F] [-G gpe_dsc] [-g grp[,...]] [--glb att_name=
att_val]] [-h] [--hdf] [--hdr_pad sz] [-L dfl_lvl] [-l path] [--mro] [--msa] [-N] [-n
loop] [--no_cll_mth] [--no_tmp_fl] [-O] [-p path] [--ppc var1[, var2[,...]]= prc]] [-R]
[-r] [--ram_all] [--rec_apn] [-t thr_nbr] [--unn] [-v var[,...]] [-w wgt] [-X box] [-x]
[-y op_typ] input-files output-file

DESCRIPTION

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.

EXAMPLES

Average files 85.nc, 86.nc, ... 89.nc along the record dimension, and store the results
in 8589.nc:
ncra 85.nc 86.nc 87.nc 88.nc 89.nc 8589.nc
ncra 8[56789].nc 8589.nc
ncra -n 5,2,1 85.nc 8589.nc
These three methods produce identical answers.

Assume the files 85.nc, 86.nc, ... 89.nc each contain a record coordinate time of length
12 defined such that the third record in 86.nc 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 85.nc 86.nc 87.nc 8512_8602.nc
ncra -F -d time,12,14 85.nc 86.nc 87.nc 8512_8602.nc
The file 87.nc 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 85.nc 86.nc 87.nc 858687_03.nc

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 8506_8906.nc

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