On Wed, Jan 04, 2006 at 07:36:17AM +0100, Poul-Henning Kamp wrote: > In message <[EMAIL PROTECTED]>, Neal McBurnett writes: > >On Tue, Jan 03, 2006 at 08:32:08PM +0100, Poul-Henning Kamp wrote: > >> If we can increase the tolerance to 10sec, IERS can give us the > >> leapseconds with 20 years notice and only the minority of computers > >> that survive longer than that would need to update the factory > >> installed table of leapseconds. > > > >Do you have any evidence for this assertion? > > It is an educated guess. > > The IERS have already indicated that they belive they could do prediction > under the 0.9 second tolerance with two or three year horizon.
The Torino Colloquium had some discussion of this. Proceedings of the Colloquium on the UTC Timescale held by ITU-R SRG 7A http://www.ien.it/luc/cesio/itu/ITU.shtml Prediction of Universal Time and LOD Variation D. Gambis and C. Bizouard, (IERS) http://www.ien.it/luc/cesio/itu/gambis.pdf After a bunch of nice graphs (not all of which were easy to interpret) I found the periodogram (essentially a discrete Fourier transform of the input data) interesting. The way I read it (expert advice welcomed), the broad peaks at 26 years (0.6 ms/d) and 52 years (0.3 ms/d) suggest that the most common pattern is a gradual cycle a few decades long of lengthening and shortening of the day, presumably driven by movements in the earth's mantle and core. Page 14 of the pdf has a table: Skill of the UT1 prediction statistics over 1963-2003 Horizon Prediction accuracy in ms 3 years 308 2 years 163 1 year 68 180 days 36 90 days 21 30 days 7 10 days 3 Perhaps these are worst cases? It would be nice to have confidence intervals. They presented these conclusions: Possibility to predict UT1 with a 1s accuracy at least over 4 years using a simple method : seasonal, bias and drift. New prediction methods are under investigation (Singular Spectrum Analysis, neural network,..) Possibility to use Core Angular Momentum prediction for decadal modeling Steve Allen wrote: > http://www.ucolick.org/~sla/leapsecs/McCarthy.html > > This deserves discussion and analysis and explanation. I wrote Dennis McCarthy about that, and he said he'd look up the details and get back to me next week. But he did remind me of this, which I remember seeing in data they published via ftp years ago: > Regarding the accuracy of these long-term predictions, the IERS > Rapid Service and Prediction Center located at the U. S. Naval > Observatory does make predictions of Delta-T in the IERS Annual > Report. The algorithm for those predictions was determined > empirically by testing a wide range of possibilities. It is > essentially an auto-regressive model using the past ten years of > data. The accuracy based on comparison of observations with what > would have been predicted using that model is shown in the table > below. Note that the accuracy estimates are 1-sigma estimates and > that excursions of 2-sigma (or more) may not be unexpected. > > +-----------------------------------------+ > |Year in the Future|Accuracy (1s) (seconds| > |------------------+----------------------| > | 1 | .04 | > |------------------+----------------------| > | 2 | .08 | > |------------------+----------------------| > | 3 | .3 | > |------------------+----------------------| > | 4 | .8 | > |------------------+----------------------| > | 5 | 1. | > |------------------+----------------------| > | 6 | 2. | > |------------------+----------------------| > | 7 | 2. | > |------------------+----------------------| > | 8 | 3. | > |------------------+----------------------| > | 9 | 4. | > +-----------------------------------------+ The http://www.iers.org/ points eventually to http://141.74.1.36/MainDisp.csl?pid=47-25786 but the links from there to the annual reports seem broken right now. I still haven't seen any good data on predictions for periods of longer than 9 years. Neal McBurnett http://bcn.boulder.co.us/~neal/
