[LEAPSECS] What happened in the late 1990s to slow the rate of leap seconds?

[Steve Allen]

On Sun 2015-11-08T18:51:37 -0800, Hal Murray hath writ:
> Was there a geological incident that explains things?

The crust of the earth has accelerated its rate of rotation during
most of the past 100 years.  The slowest rotation ever was around
1912, and since then it has been rotating faster.  By happenstance,
the rate of rotation of the crust was at a local minimum in 1972 at
the inception of leap seconds, and since then it accelerated again.

> There is another warp in the graph in the late 1980s.  Things slowed down for
> several year, but not as dramatically as the early 2000s.

Don't look at the graph of Delta T, that's effectively the integral of
the rate of rotation and its smoothness hides what the slope is
telling you.  Look at the graph of Length of Day.  That
integral/derivative pair are the first two graphs at
http://www.ucolick.org/~sla/leapsecs/amsci.html

For a historic view of the LOD going back 2000 years look at the plots on
http://www.ucolick.org/~sla/leapsecs/dutc.html

--
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