On 2020-01-27 11:52 AM, Steve Allen wrote:
On Mon 2020-01-27T19:33:37+0000 Tony Finch hath writ:
It looks like we're in another long gap, based on the LOD chart and the
UT1-UTC prediction. The current gap is now the second longest...
In the middle of last year the rotation of the earth accelerated
enough that LOD went below 86400 for several weeks, and DeltaT
decreased significantly.
https://datacenter.iers.org/singlePlot.php?plotname=FinalsDataIAU2000A-UT1-UTC-BULA&id=10
https://datacenter.iers.org/singlePlot.php?plotname=FinalsDataIAU2000A-LOD-BULA&id=10
The LOD effects are easier to see using the plots from the Paris
bureau of IERS by requesting to remove the predictable tidal
variations that basically look like noise on the second plot here.
I've been studying DUT1, the 1/10th second "mini leaps", mandated by
ITU-R Recommendation 460, produced by IERS in Bulletin D
(ftp://ftp.iers.org/products/eop/bulletind/), and disseminated by the
time radio broadcasts (WWVB, DCF77, MSF and such). This is another way
to look at the trends Steve has pointed out.
The Bulletin D publications in the IERS folder go back only to
1991-06-20. I obtained the full inventory since UTC1972 from an
authoritative source. I assembled an Excel to examine the distribution
of intervals (called spans) between of the DUT1 dates.
Worksheet "BulD_Spans" shows the DUT1 span lengths in (UTC) days (Y)
v.s. the nth DUT1 change (X), and Excel "trend lines". Worksheet
"UTC_Spans" shows the leap-seconds similarly.
http://edlmax.com/Common_Calendar/BulD_and_UTC_Spans.xls
The trend lines show a continuing increase of the "span" lengths between
DUT1 changes and leap-seconds.
The most recent Bulletin D DUT1 change, from -0.1s to -0.2s, occurred on
2019-05-02. Examining UT1 predictions from Bulletin A
(ftp://ftp.iers.org/products/eop/rapid/bulletina/bulletina-xxxiii-003.txt)
indicates the next DUT1 change may not happen until 2020-11-10 when
UT1-UTC crosses -0.25000. This will be a DUT1 span of 558 days. This is
far longer than the longest earlier DUT1 span of 392 days that occurred
during the 1999 to 2006 "leap-second drought".
UT1-UTC must reach -0.5s before a leap-second will be announced. If
these trends hold it could be quite a while, perhaps years, before the
next leap-second.
(Note that IERS does not use Bulletin A UT1-UTC prediction values for
determining DUT1 and leap-seconds but rather from EOP C04
(http://hpiers.obspm.fr/iers/series/opa/eopc04_IAU2000). This is the
internal data set IERS assembles and is NOT the official 'product'.
Bulletin A is the official publication. Note Bulletin A gives UT1-UTC to
5 points of precision while C04 gives 7 points.)
Predicting the future is an inherently risky business.
-Brooks
--
Steve Allen<[email protected]> WGS-84 (GPS)
UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855
1156 High Street Voice: +1 831 459 3046 Lng -122.06015
Santa Cruz, CA 95064https://www.ucolick.org/~sla/ Hgt +250 m
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