The data I used came from USNO/IERS, and were reduced using standard formulas from the IERS Conventions.
But I have published an LOD plot of Stephenson's data, going back to ~1770, with Allan deviations, here: https://www.gps.gov/cgsic/meetings/2014/matsakis.pdf <https://www.gps.gov/cgsic/meetings/2014/matsakis.pdf>. It shows a speed up of comparable magnitude (but less width) at around 1870 followed by a larger slow down around 1900. The speed-up after that slowdown is roughly comparable to what we are seeing now. Sorry, but I have not tapped into a mother-load of modern studies, although people are always Fourier-transforming these things. I am impressed by recent reports of seismic data indicating large blobs at the core-mantle boundary. All my life I’ve heard motions down there are the possible cause of these fluctuations. I can’t tell you how the numbers work out, but see this: "As part of the EGU General Assembly 2021 (https://www.egu2021.eu/ <https://www.egu2021.eu/>) that will be held virtually from 19 to 30 April 2021, we like to draw your attention to session G3.1: Earth Rotation: Theoretical aspects, observation of temporal variations and physical interpretation (https://meetingorganizer.copernicus.org/EGU21/session/39900 <https://meetingorganizer.copernicus.org/EGU21/session/39900>). Below you can find the detailed description." > On Jan 12, 2021, at 9:01 PM, Seaman, Robert Lewis - (rseaman) > <rsea...@arizona.edu> wrote: > > Are there citations, from F. R. Stephenson or otherwise, constraining whether > such dramatic short-term reversals are physically anticipated? If so, would > this then increase the likelihood of a subsequent period of (relatively) > rapid correction back to the general overall slowing trend? Which is to say > do we have a handle on the power spectrum of various terms (annual, decadal, > longer)? (Undoubtedly I’m expressing that naively, feel free to rephrase the > above questions.) > > Rob > > From: LEAPSECS <leapsecs-boun...@leapsecond.com > <mailto:leapsecs-boun...@leapsecond.com>> on behalf of Demetrios Matsakis via > LEAPSECS <leapsecs@leapsecond.com <mailto:leapsecs@leapsecond.com>> > Reply-To: Leap Second Discussion List <leapsecs@leapsecond.com > <mailto:leapsecs@leapsecond.com>> > Date: Tuesday, January 12, 2021 at 6:20 PM > To: "leapsecs@leapsecond.com <mailto:leapsecs@leapsecond.com>" > <leapsecs@leapsecond.com <mailto:leapsecs@leapsecond.com>> > Cc: Demetrios Matsakis <dnmyia...@yahoo.com <mailto:dnmyia...@yahoo.com>> > Subject: [EXT][LEAPSECS] Five years to go? > > I attach a plot of my extrapolations, which take into account known periodic > oscillations to predict that if the Earth continues to rotate as the same > rate it has for the last 100 days, a negative leap second will be “needed" in > five years. > > The word file shows what the attached plot is based on. > <image001.jpg> > _______________________________________________ > LEAPSECS mailing list > LEAPSECS@leapsecond.com <mailto:LEAPSECS@leapsecond.com> > https://pairlist6.pair.net/mailman/listinfo/leapsecs > <https://pairlist6.pair.net/mailman/listinfo/leapsecs>
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