[LEAPSECS] Crunching Bulletin B numbers
Warner Losh
imp at bsdimp.com
Tue Feb 15 16:31:49 EST 2011
On 02/15/2011 09:12, Rob Seaman wrote:
> So, what is the state of the art for long term predictions of UT1? Could the algorithms used by the EOP PCC teams simply be run on the historical Bulletin B numbers to find out?
At the Torin conference they had a sliding scale for confidence in UT1
predictions, and it was very non-linear. I don't have the reference
handy, but it went something like:
10 days a few microseconds
100 days a few milliseconds
1000 days a second or two
which fits with other statements that said operationally, they can model
the earth well enough to predict leap seconds about 2-3 years into the
future with a 98% confidence level to conform with the DUT1 .9s requirement.
Looking at the Bulletin B's might not give a long enough time horizon.
Those only predict out 30 days or so. There's other time products that
have modeled numbers out farther than that.
Bulletin A, for example gives formulas like the following that could be
graphed historically to see how well or poorly they have done:
UT1-UTC = -0.1584 - 0.00068 (MJD - 55610) - (UT2-UT1)
UT2-UT1 = 0.022 sin(2*pi*T) - 0.012 cos(2*pi*T)
- 0.006 sin(4*pi*T) + 0.007 cos(4*pi*T)
where pi = 3.14159265... and T is the date in Besselian years.
IERS provides historical aggregated earth orientation data that can be
used to see how well predictions match actual data over any given time
horizon.
There's enough grunt work here that you might be able to publish a paper
on this. :)
Warner
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