@martinjuckes My perspective is that we will continue to honor SI seconds and days, weeks, and fortnights (2 weeks) as integer multiples of SI seconds. The thing that can be quite confusing in all this is that the number of seconds that has elapsed since any given epoch is the same in both the UTC and TAI time systems. The time stamps for the epoch may be different, but the elapsed time is always exactly the same. The same is true of 360-day, lunar, 365-day, Julian, and Gregorian calendars, when used in the real world. The date stamp for a given epoch will be different in each, but the number of days that have elapsed since that epoch will be the same in all the calendars.
Leap days and leap seconds are a mechanism to keep the date and time stamps synchronized with the orbital and rotational motion of the earth relative to the sun. Adding leap days to date stamps keeps the Vernal Equinox to within one day of the same month and day. Adding leap seconds to time stamps keeps midnight at 0 degrees longitude to within one second of the same hour, minute, and second. Leap days and seconds are only about time stamps, not about how much time has passed. The Gregorian calendar says, "Let's keep the months and days lined up with the seasons." The UTC time system says, "Let's also keep the hours and minutes lined up with the solar days." The TAI time system says, "Let's let the hours and minutes do their own thing and slip relative to solar days." When we had this discussion on the CF metadata listserv a few years ago, I started out advocating for a new calendar that would be entirely TAI, so epoch time stamps would be in TAI. This meant we would need three new calendars instead of two. I became convinced that the side effects of this would cause more problems than it would solve. Users who didn't realize that the TAI epoch time stamps were not UTC (or didn't go to the trouble of getting leap-second-aware software to get time stamps from the time variable) would have maximal discrepancy between the times they thought they had and the actual times (different amounts in different years up to 37 seconds for data from 2017 and 2018). Data producers who want to store monotonic, metric elapsed times in their time variables won't find it hard to generate accurate UTC time stamps for their time variable epochs, so there didn't seem to be a compelling case for giving people the option of going "full TAI". -- You are receiving this because you commented. Reply to this email directly or view it on GitHub: https://github.com/cf-convention/cf-conventions/issues/148#issuecomment-435086285
