CODEWITHSUNDEEP
rnetcdfnco
zoek
zoek

Reputation: 151

Change units of time dimension in NetCDF file from months to months since

I currently have multiple NetCDF files with 4 dimensions, (latitude, longitude, time, and depth). Each represents a single year of monthly data. The unit of time is "month", 1-12, and therefore quite useless if I want to merge these files across years to give me a single NetCDF file with a time dimension of size months*years.

The time dimension attributes for a single file:

time  Size:12   *** is unlimited ***
            long_nime: time
            units: month

I used ncrcat of nco to merge.

ncrcat soda3.3.1*sst.nc -O soda3.3.1_1980_2015_sst.nc

This works except that when merged, time values read 

#in R
soda.info$var$temp$dim[[3]]$vals
  [1]  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1
 [26]  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2
 [51]  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3
 [76]  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4
[101]  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5
[126]  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6
[151]  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7
[176]  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8
[201]  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9
[226] 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10
[251] 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11
[276] 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12
[301]  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1
[326]  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2
[351]  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3
[376]  4  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4
[401]  5  6  7  8  9 10 11 12  1  2  3  4  5  6  7  8  9 10 11 12  1  2  3  4  5
[426]  6  7  8  9 10 11 12

...which obviously isn't much help if I want to keep track of time.

In the past I've only used NetCDF files with a "months since..." unit. Is there a way to change these rather groundless 'month' units to 'months since...'?

Upvotes: 2

Views: 1059

Answers (1)

Charlie Zender
Charlie Zender

Reputation: 6352

Would it suffice to enumerate the months sequentially?

ncap2 -s 'time=array(0,1,$time)' soda3.3.1_1980_2015_sst.nc out.nc

You can also add a "months since ..." unit to time as described in the comment by Chelmy and/or in the NCO manual. I leave that as an exercise for you, gentle reader.

Upvotes: 2

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