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3.20 Rebasing Time Coordinate

Availability: ncra, ncrcat Short options: None

Time rebasing seeks to fix the following problem. we have a bunch files to concatenate or average along a common record dimension/ coordinate. The thing is although the record coordinate is in the same time units in each file the date offset is different.
For example suppose the time co-ordinate is in hours and we have 31 files for each day in january. Witin each file is the variable temperature temp(time); and a time co-ordinate that goes from 0-23 hours. The time:units attribute from each file is as follows

     file01.nc -- time:units="hours since 1990-1-1"
     file02.nc -- time:units="hours since 1990-1-2"
     file03.nc -- time:units="hours since 1990-1-3"
     file04.nc -- time:units="hours since 1990-1-4"
     ...
     ...

     //Find the mean noon day temperature in january
     ncra -v temp -d time,"1990-1-1 12:00:00","1990-1-31 23:59:59",24 \
           file??.nc noon.nc
     
     // concatenate day2 noon - day3 noon records
     ncrcat -v temp -d time,"1990-1-2 12:00:00","1990-1-3 11:59:59" \
           file01.nc file02.nc file03.nc noon.nc
     
     // As you can see the time has been "rebased" to the time units in "file01.nc"
     time=36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52,
          53, 54, 55, 56, 57, 58, 59 ;
     
     // If we repeat the above command but with only two input files
     ncrcat -v temp -d time,"1990-1-2 12:00:00","1990-1-3 11:59:59" \
           file02.nc file03 noon.nc
     
     // then the output time coordinate is "based" on the time units in "file02.nc"
     time = 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
         29, 30, 31, 32, 33, 34, 35 ;