missing value changes using duration feature

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2013-12-03
2013-12-11
  • Andrew Friedman

    Andrew Friedman - 2013-12-03

    Hi,

    I'm calculating the annual mean of a monthly SST dataset with the following syntax using the duration feature:

    ncra -O -F --mro --dmn time,1,,12,12 infile.nc outfileAVG.nc

    However, some of the missing values of my dataset seem to be changed in the averaging.

    When I examine the outfile, some of the values of "_," from the infile appear as "Infinityf" in the outfile.

    This problem does not seem to occur when I do a simple "ncra" on the whole input file without the duration feature.

    This is how _FillValue is defined in the input file:
    float sst(time, latitude, longitude) ;
    sst:_FillValue = -1.e+30f ;

    Any ideas what is going on?

    I'm running nco 4.3.8 and netcdf 4.3.0 on MacOS 10.9.

    I've posted links to the files here:
    https://dl.dropboxusercontent.com/u/647140/infile.nc
    https://dl.dropboxusercontent.com/u/647140/outfileAVG.nc
    (infile.nc is a selection from the HadSST3 dataset):
    http://hadobs.metoffice.com/hadsst3/data/download.html

    Thanks,
    Andrew

     
  • Charlie Zender

    Charlie Zender - 2013-12-03

    Hmm. I see what you mean from the output file that you posted.
    However, I am unable to reproduce the results in Linux from the input file you posted. Under Linux, with the just-released 4.3.9, I get a normal output file with not Infinity's. This is likely a bug. Thank you for reporting it. Will post more when I know more.
    cz

     
  • Charlie Zender

    Charlie Zender - 2013-12-11

    I now understand what causes the problematic behavior you encountered. I think the bug was introduced in NCO 4.3.6 in September. I'm still thinking how best to fix it. In the meantime, I think this workaround may work for your case: add the switch --flt to the command. Please let me know if this does not work. Will post more when I've committed a fix.
    cz

     
  • Charlie Zender

    Charlie Zender - 2013-12-11

    OK, I just committed a tentative fix to this problem. Would appreciate any feedback on whether it works for you. Thanks!
    cz

     
  • Andrew Friedman

    Andrew Friedman - 2013-12-11

    Thank you Charlie! The averaging works properly with the switch --flt. I'll let you know how the committed version works when I update NCO.
    Best, Andrew

     

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