updated to 4.9.7 and mro is not working

[John]

We just updated NCO to 4.9.7 and mro is not working correctly.

ncra --mro -d time,,,12,12 in.nc out.nc

The command runs but out.nc has only 1 time slice, the average of all the time slices (and the value of the average is correct). I'm really hoping to use the per_record_weights option offered by 4.9.7! How could we troubleshoot this?

Is the input file somehow not structured right? It looks like this:

netcdf in {
dimensions:
    lat = 1 ;
    lon = 1 ;
    time = UNLIMITED ; // (1140 currently)
variables:
    double lat(lat) ;
       // snip
    double lon(lon) ;
      // snip
double time(time) ;
        time:units = "days since 1900-01-01 00:00:00" ;
        time:long_name = "time" ;
        time:calendar = "standard" ;
        time:missing_value = 1.00000001504747e+30 ;
        time:bounds = "time_bnds" ;
        time:axis = "T" ;
        time:standard_name = "time" ;
        time:cell_methods = "time: mean" ;
    float tmin(time, lat, lon) ;
        tmin:_FillValue = 1.e+30f ;
        tmin:missing_value = 1.00000001504747e+30 ;
        tmin:units = "K" ;
}

Returning from a hiatus... so am feeling a little rusty. Thank you.

[John]

Found a workaround after a lot of voodoo!

First, I discovered that mro works OK on some of my files. So I compared the metadata of the working & non-working files and could not find any difference. I also tried extracting smaller slabs and -- weirdly -- some of the small slabs worked with mro and some didn't.

I then tried running "ncra --mro" with the debug flag "-D 3", and compared the debug info between the working and non-working files. With the non-working file, debug info showed all the input time slices going into one output time slice, but it did not hint at the cause.

Finally, I tried exporting a small slab (for which mro did not work) into cdl and re-create an nc file from that using ncgen, and mro worked on the resulting file! That gave me the idea that something must be corrupt in my nc file. So I ran "ncks -3" on the file to convert it to netcdf3, thinking not so much that the version is important, but having NCO write the file out itself is important. Then I ran "ncra --mro" on the resulting file, and it's working. Phew!

Just documenting in case others run into a similar problem.

[Charlie Zender]

Thanks for the input. NCO 5.1.9 had a fix to --mro that might help your use-case. I suggest updating to the latest stable version, 5.3.6.