[LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22

Poul-Henning Kamp phk at phk.freebsd.dk
Mon Feb 7 12:55:44 EST 2011

In message <3B33E89C51D2DE44BE2F0C757C656C880A1C45AF at mail02.stk.com>, "Finklema
n, Dave" writes:

>I finally get a chance to look like I might know something.


>Neiher Gravity nor the Geoid are "standardized."

Indeed. I was surprised when I tried to confirm my recollection
about the TAI/MSL thing earlier today and didn't find anything
even remotely resembling a definition of of "MSL".

I guess the magnitudes of uncertainty this introduces are below the
noise-limit still, but I wonder if another meter of ex-polar-icecap
water would start to skew the results measurably time/frequency

There is a very interesting bit of research going on right now
trying to find out where the meltwater is/will be going, and
the results are anything but intuitive.

If all the Greenland ice melted, but the Antarctic ice didn't,
the meltwater would largely pile up around Antarctica, and generally
lower MSL on the nothern hemisphere.

Melt Antarctica and see water rise around Greenland and drop
on the southern hemisphere.

This is a counterintuitive result, until you realize that both
places a LOT of ice is sitting above MSL, exerting a significant
"upwards" gravitationa force.

I've seen some yet unpublished models which shows that an extra
meter of MSL will distribute unevenly, roughly from from 0 to 170cm,
depending on geography, but the uncertainties are still too
big to be useful for anything.

Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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