Seasonal average with ncra --mro only selecting value of first record

Question

I have files with monthly data only for September, October and November (filtered in a previous step) and I want to compute seasonal averages (one value for each trimester of each year). I'm using ncra --mro -d time,,,3,3 (average on the record dimension, from start to finish, jumping every tree records and each subcycle is 3 records) but the result is not an average of the tree months but just the value of each September.

I can confirm that by using ncks -d time,,,3 to select only the first month of each year (September in my case) and when I read both results using an external tool, they are exactly the same.

Here are the commands that I ran along with comments on the results. All the files can be here.

# Try to make a seasonal average from the orignal file
# It gets :
# ncra: WARNING Subcycle argument is only supported for the record dimension on ncra and ncrcat operations
ncra --mro -d time,,,3,3 original.nc4 average.nc4

# Select only the first month of the season
ncks -d time,,,3 original.nc4 sampled.nc4

# When I read both files (using an external tool) I see that both files are identical. That is, 
# the first command didn't actually compute an average, it just selected the first value
# of each season. 

# Perhaps it's related to the warning about the record dimension. 
# Ok, let's make sure time is a record dimension I guess?
ncks --mk_rec_dmn time original.nc4 record.nc4

# And now again try to compute seasonal average
ncra --mro -d time,,,3,3 record.nc4 record_average.nc4

# Now this new file is too small (77kb vs 928kb) and I cannot read it with any tool 

ncks --version returns: NCO netCDF Operators version "4.6.3" built by buildd on binet at Dec 23 2016 22:34:40 ncks version "4.6.3"

Answer 1

Your commands look correct to me (good job!). Below is a demonstration that your commands work with the latest version of NCO. Your version is > 5 years old! I can only surmise that something was broken in that version. Please upgrade. Charlie

zender@firn:~$ ncrcat -O -v FSNT,area -p ${DATA}/ne30/raw 20180129.DECKv1b_piControl.ne30_oEC.edison.cam.h0.0001-09.nc 20180129.DECKv1b_piControl.ne30_oEC.edison.cam.h0.0001-10.nc 20180129.DECKv1b_piControl.ne30_oEC.edison.cam.h0.0001-11.nc 20180129.DECKv1b_piControl.ne30_oEC.edison.cam.h0.0002-09.nc 20180129.DECKv1b_piControl.ne30_oEC.edison.cam.h0.0002-10.nc 20180129.DECKv1b_piControl.ne30_oEC.edison.cam.h0.0002-11.nc ~/FSNT_000109_000211.nc
zender@firn:~$ ncks --cal -v time -C  ~/FSNT_000109_000211.nc
netcdf FSNT_000109_000211 {
  dimensions:
    time = UNLIMITED ; // (6 currently)

  variables:
    double time(time) ;
      time:long_name = "time" ;
      time:units = "days since 0001-01-01 00:00:00" ;
      time:calendar = "noleap" ;
      time:bounds = "time_bnds" ;
      time:cell_methods = "time: mean" ;

  data:
    time = "0001-10-01", "0001-11-01", "0001-12-01", "0002-10-01", "0002-11-01", "0002-12-01" ;

} // group /
zender@firn:~$ ncra -O --mro -d time,,,3,3 ~/FSNT_000109_000211.nc ~/FSNT_SON_000109_000211.nc
zender@firn:~$ ncwa -O -w area -a ncol ~/FSNT_000109_000211.nc ~/FSNT_glb_avg.nc
zender@firn:~$ ncwa -O -w area -a ncol ~/FSNT_SON_000109_000211.nc ~/FSNT_SON_glb_avg.nc
zender@firn:~$ ncks -H -v FSNT -C ~/FSNT_glb_avg.nc
netcdf FSNT_glb_avg {
  dimensions:
    time = UNLIMITED ; // (6 currently)

  variables:
    float FSNT(time) ;

  data:
    FSNT = 241.5002, 242.7969, 244.3921, 241.2065, 242.6262, 242.8979 ;

} // group /
zender@firn:~$ ncks -H -v FSNT -C ~/FSNT_SON_glb_avg.nc
netcdf FSNT_SON_glb_avg {
  dimensions:
    time = UNLIMITED ; // (2 currently)

  variables:
    float FSNT(time) ;

  data:
    FSNT = 242.8964, 242.2435 ;

} // group /
zender@firn:~$