[LEAPSECS] This year's Y2K: 'Leap second' threatens to break the Internet -Brooks

Steve Allen sla at ucolick.org
Thu Jan 15 09:46:40 EST 2015

On Thu 2015-01-15T03:24:43 +0000, Alex Currant via LEAPSECS hath writ:
> The ITU link says there will be 2-3 minutes discrepancy by 2100.
> At the current rate of 1 every 3 years, we would expect 80/3, or
> 26.667 seconds discrepancy.  I have found a reference which
> estimates the effect of the tidal slow-down and predicts that the
> discrepancy will still be less than a minute:
> http://www.gps.gov/cgsic/meetings/2014/matsakis.pdf
> See the third backup viewgraph and the first six of the
> presentation.
> Steve Allen's web pages have values that are much larger.�

People have liked to suppose that the change of Length of Day is
linear over time, a constant deceleration.

See the first plot of Length of Day on
The LOD change since Alexander the Great is not linear.
It is only approximately matched by any of the three lines.
Matsakis points out that looking only at the past two centuries the
LOD is pretty much a random walk.  This is clearly visible in the
zoomed plots on that web page.

A linear change in Length of Day results in a quadratic accumulation
of Delta T.  See the penultimate plot on
The Delta T since Alexander the Great is not quadratic.
It is only approximately matched by any of the three parabolae.

> Who is right?

The short term LOD variations (weeks or less) have been very well
modelled by weather in the atmosphere since I was doing VLBI at JPL
in the 1980s.  Big snowstorms make visible changes.

Richard Gross at JPL has a model of ocean currents which does pretty
good at modelling the annual variations which are conventionally
described in the equations for UT2-UT1.  That's weather too.

The decadal fluctuations have been huge and must be caused by changes
in the body and or core of the earth.

There's a quote (where academics argue about its attribution)
"Prediction is hard, especially about the future."
Being "right" means predicting the weather in the core of the earth
for the next century.  I make no such claim.  I have merely plotted
out the numbers in the literature.  Pick your favaorite number.

Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
UCO/Lick Observatory--ISB   Natural Sciences II, Room 165    Lat  +36.99855
1156 High Street            Voice: +1 831 459 3046           Lng -122.06015
Santa Cruz, CA 95064        http://www.ucolick.org/~sla/     Hgt +250 m

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