[LEAPSECS] Predicting the next leap second

[Tom Van Baak]

Demetrios -- Thanks for posting that. It would make sense that IERS uses 
UT2 to better look for trends. But the UTC spec is based on UT1 so I can 
see how that could be awkward.

List members -- His posting contained a wonderful plot as an inline / 
attachment named "UT1and UT2S.jpg". If you did not see the plot in your 
copy of the posting a few hours ago, please send a note to: 
leapsecs-owner at leapsecond.com so that we can debug the problem.

I will attach another copy of his plot to this posting, just in case.

Thanks,
/tvb

[ sent as plain, with UT1-and-UT2S.jpg as attachment ]


On 8/23/2020 5:08 PM, Demetrios Matsakis via LEAPSECS wrote:
> Here is  a plot that might interest some of you.  The blue curve  is  
> UT1-UTC, and you can see when the last leap second was inserted.  The 
> goal is to be sure it never goes below -0.9, and the IERS obviously 
> took no chances back then.   But remember that if they are making a 
> decision 5 months in advance, the time of interest is 11 months 
> later.   (The decision made last July was to forestall being too 
> negative on the next June 30.)
>
> But UT1-UTC is distorted by seasonal and lunar terms (the largest one 
> being a 19 year cycle, with peak to peak about 0.3 seconds).  You can 
> see a seasonal variation in the blue curve.  The red curve shows what 
> happens if you take them out (the formulas are in the IERS Standards). 
>   To predict what the IERS will decide about a possible June 30 leap 
> second next year, I recommend you take your attention from the blue to 
> the red, decide how to extrapolate the red curve to December 2021, and 
> then map it back to the blue.   Then you can place your bet.  But will 
> you win?  Don't ask me.
>
> Demetrios, who is actually being paid to work on predicting this kind 
> of thing.
>
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