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
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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.
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Christopher Lynnes
Goddard Earth Sciences Data and Information Center, NASA/GSFC
301-614-5185
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--
Jim Biard
Government Contractor, STG Inc.
Remote Sensing and Applications Division (RSAD)
National Climatic Data Center
151 Patton Ave.
Asheville, NC 28801-5001
[email protected]
828-271-4900
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