If you go back I'm sure you'll see it mentioned in the LEAPSECS archive.
When you play with 1962+ data there's a clear ~20 year cycle [1] and,
more importantly, LOD ends up a bit lower each cycle. So the general
pattern looks like 20 year arcs back-to-back on top of a gradual trend
of ELOD going from 2 or 3 ms to 1 or 0 ms the past 60 years.
These arcs are why there's a leap second lull or drought every ~20 years
and that's why this time around there is even talk about a negative leap
second. Even if we just barely escape a negative leap second this cycle,
the trend says we will get one for sure before the end of the next ~20
year cycle.
This has nothing to do with "tidal braking" which is extremely
long-term, as in astronomical timescales. Over decades or perhaps
centuries the not-fully-understood cycles internal to the dynamic earth
have greater impact.
/tvb
[1] Demetrios has mentioned its the 6939 day Metonic cycle:
https://en.wikipedia.org/wiki/Metonic_cycle
On 7/26/2022 4:33 PM, Poul-Henning Kamp wrote:
So looking at the IERS LOD plot going all the way back it seems to
me that we have been missing the big signal for about five decades:
https://datacenter.iers.org/singlePlot.php?plotname=EOPC04_14_62-NOW_IAU2000A-LOD&id=224
How did we not notice that earlier ?
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