I have encountered an issue with using a negative year in the units attribute of time variables in NetCDF files. The interpretation in cftime (Python) is that year zero does not exist, while in other software such as Panoply the interpretation is that year zero exists. This affects how the time variable is read and displayed, and effectively causes one year difference between the different implementations. The CF Conventions (Section 4.4. Time Coordinate) do not explicitly state how negative years should be treated, except for stating that year 0 has a special meaning. On the contrary, ISO 8601, seems to be more on the side of including year 0.
In particular, this issues comes up when using Julian date in NetCDF files, which has a reference time of 1 January 4713 BCE, 12:00 UTC. As of now it is impossible to use it in NetCDF files and get consistent results in Python (through the netCDF4 package) and Panoply. I suppose there are multiple possible solutions to the problem. Either all implementations start using the same method of counting negative years (and it would be helpful if the CF Conventions make this unambiguous), or there would have to be information about the year numbering convention included in the NetCDF file, such as a new attribute or an indicator included in the `units` or `calendar` attributes. Related issue in cftime: [#200](https://github.com/Unidata/cftime/issues/200). -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/cf-convention/cf-conventions/issues/298 This list forwards relevant notifications from Github. It is distinct from cf-metad...@cgd.ucar.edu, although if you do nothing, a subscription to the UCAR list will result in a subscription to this list. To unsubscribe from this list only, send a message to cf-metadata-unsubscribe-requ...@listserv.llnl.gov.
