Availability:
ncra, ncrcat
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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 ;