Several tasks relating to manipulating netCDF files and dates/times within them are noted here.

1. Converting the units and values of the time variable.

Setting the time ‘axis’

I have a netcdf file that contains a time variable. The values in the variable’s data array represent time units since date time string. Some model output and data formats use months since as the unit, which strictly speaking is non-standard and not CF compliant. (The integer values in the time variable array simply count increasing months, for example.)

Instead, I would like these to be represented as days since. So the integer values for time should now represent months.

I also want the month value to be reperesented at the mid-point of the month (The 15th), so I have chained in the -settaxis command as well.

cdo settunits,days -settaxis,2001-01-15,00:00,1month INFILE.nc NEW_OUTFILE.nc

The command settunits will change the time:units value as well, if it is in standard CF format.

It is useful to check the output is correct using cdo showdate or cdo showdatetime

2001-01-15  2001-02-15  2001-03-15  2001-04-15  2001-05-15....