Hi.
According to the almighty Wikipedia ;), UTC is "a time standard based on
International Atomic Time
<
http://en.wikipedia.org/wiki/International_Atomic_Time> (TAI) with leap
seconds <
http://en.wikipedia.org/wiki/Leap_second> added at irregular
intervals to synchronize with the Earth's rotation
<
http://en.wikipedia.org/wiki/Earth%27s_rotation>." So TAI doesn't
attempt to stay synchronized with the Earth's rotation.
Another quote from the Wikipedia article on UTC states
UTC is a discontinuous timescale, so it is not possible to compute
the exact time interval <
http://en.wikipedia.org/wiki/Time> elapsed
between two UTC timestamps without consulting a table that describes
how many leap seconds occurred during that interval. Therefore, many
scientific applications that require precise measurement of long
(multi-year) intervals use TAI
<
http://en.wikipedia.org/wiki/International_Atomic_Time> instead.
I'm not advocating for anything, just contributing some factoids.
Grace and peace,
Jim Biard
On 8/23/2011 8:13 AM, Lynnes, Christopher S. (GSFC-6102) wrote:
> On Aug 22, 2011, at 6:36 PM, John Caron wrote:
>
>> On 8/22/2011 6:37 AM, Jonathan Gregory wrote:
>>> Dear Chris
>>>
>>>> Perhaps there could be an attribute we could set that says whether we have accounted for leap seconds? With the absence of such an attribute to be presumed as meaning leap seconds have been ignored.
>>> Perhaps the real-world calendars with and without leap seconds should be
>>> regarded as two different calendars, since they have different encodings
>>> (meaning decoding/encoding as YMD HMS<-> time-interval since reference-time).
>>> The "true" real-world calendar is the one with leap seconds.
>>>
>>> CF has a calendar
>>> proleptic_gregorian
>>>
>>> A Gregorian calendar extended to dates before 1582-10-15. That is, a year is a leap year if either (i) it is divisible by 4 but not by 100 or (ii) it is divisible by 400.
>>>
>>> What if we clarified this calendar as not having leap seconds? Then it could
>>> be used for real-world applications for recent dates meaning that it was just
>>> like the real world except that it doesn't have leap seconds.
>>>
>>> Model calendars, which are already idealised wrt length of year, don't have
>>> leap seconds anyway, I am sure.
>>>
>>> Best wishes
>>>
>>> Jonathan
>>> _______________________________________________
>>> CF-metadata mailing list
>>> CF-metadata at cgd.ucar.edu
>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>> I agree that a separate calendar is needed if we want to have leap
>> seconds. I think the common form is UTC (or TAI?). Chris, what does the
>> satellite community use?
> Both UTC and TAI, actually.
>
>> _______________________________________________
>> CF-metadata mailing list
>> CF-metadata at cgd.ucar.edu
>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
> Christopher Lynnes
> Goddard Earth Sciences Data and Information Center, NASA/GSFC
> 301-614-5185
>
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
--
Jim Biard
Government Contractor, STG Inc.
Remote Sensing and Applications Division (RSAD)
National Climatic Data Center
151 Patton Ave.
Asheville, NC 28801-5001
jim.biard at noaa.gov
828-271-4900
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