[LEAPSECS] Crunching Bulletin B numbers

[Warner Losh]

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://six.pairlist.net/pipermail/leapsecs/attachments/20110215/6b5ebeb4/attachment.html>