Serbian Astronomical Journal, including mention of negative leap secondshttp://arXiv.org/pdf/0808.3612
Timekeeping is one of those narrow disciplines where peer review implies small number statistics. So this paper joins others of suspect validity such as:
Deines & Williams (2007, AJ, 134, 64) "Time Dialation and the Length of the Second: Why Timescales Diverge"
That said, it doesn't appear to be devoid of content - simply rather "lazy". I'm particularly taken with statements like "all the physical factors unambiguously recognized till nowadays cannot cause such a phenomenon". Most journal editors and referees would have a hard time accepting a paper with such a conclusion. Rather, the authors' curiosity should have driven them to further investigation of one sort or another. Either tie the results to the current physical basis of the field, or acquire data sufficient to call current physical understanding into question.
One is left wondering how this paper came to be written. PHK's supposition about undergrads sounds about right. Some of the choice of wording seems to imply that the authors are directly or indirectly aware of discussions from this mailing list. The title suggests an interest in abetting the ITU-R's agenda. The shallow analysis (and obscure journal) should make this all rather moot. I am pleased, however, to see some attempt at predicting Earth orientation, but this surely cannot represent the state of the attainable art :-)
I can't add much to the previous comments that a fit with so many degrees of freedom is immediately suspect for purposes of extrapolation. It is unremarkable that they were able to track every tiny wiggle in the data. FIgure 4 is quite humorous.
Modeling delta-T, a cumulative effect, doesn't seem very expressive in general - all the empirical insight was smoothed out of the data before they started. Rather, it would be better to focus on LOD or other more direct indicators of Earth orientation or rotation rate. Integrate the models to recover UT1, etc., as a separate step. A fit without residuals is like signal with no noise - begging for skepticism.
One could seek physical explanations for the more (statistically) significant harmonic terms. For example, the 22 year period is twice the solar cycle and there could be coupling with the magnetic field reversals. A few of the terms in this (apparently) unconstrained fit pop out near annual, fractional annual, and multi-annual periods. Probably not a coincidence. The solar system is rife with harmonic resonances of various sorts. Surely the Earth rotation community must have considered a number of such phenomena previously given that lunar tidal locking is recognized as the principal driver for Earth's rotational slowing?
On the other hand, understanding the short period seasonal effects on LOD (all those beautiful wiggles from the plots on Steve Allen's web site, for instance) benefits simply from coverage over many cycles. It has taken a century or two to figure out the solar cycle due to its long period. Long term LOD phenomena will take similarly long to sort out. A comparative study with LOD data from the other planets and satellites could be revealing. (One suspects the available data aren't sufficiently precise for the other planets. Sounds like a good argument to send astronomers to Mars :-)
The 222 year period is most likely a meaningless artifact of the data. The long term trend of tidal slowing is going to pop out as the most significant term. The corresponding period is truncated by the truncated horizon of the available data.
Would prefer to see a similar fit with fewer terms and more constraints. How about forcing terms with periods of a lunar month, a solar year, etc? In addition to the free harmonic terms, how about an explicit linear trend forcing the long term tidal slowing? How about forcing the millennial term from http://www.ucolick.org/~sla/leapsecs/ancient.pdf? How about estimating the magnitude of the coupling between the terrestrial magnetic field and the solar magnetic field? Could this possibly transfer enough angular momentum to affect the Earth's rotation?
This particular paper is only worth attention due to the dearth of similar papers.
Rob Seaman NOAO
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