On Sat 2018-10-06T16:42:23-0700 Paul Eggert hath writ:
Steve Allen wrote:
This is definitely true in this era. Assuming (bad thing to do) that rotation of the crust does not undergo another strong deceleration the two dates per year should be enough for the next 40 years.
My eyeballing of the "extrapolated long-term trend" of Figure 18 of Stephenson et al. 2016 says that 2 leap seconds per year should be enough until 2300 or so.
The red band is the long term average, and two leap seconds per year is an excess LOD of about 5.4 ms, so that shows around year 2100. The green curve should be taken with a huge grain of salt because none of the decadal fluctuations are mapped prior to the 1800s. https://link.springer.com/article/10.1007/s00190-006-0067-3 Huber, P.J. J Geodesy (2006) 80: 283. https://doi.org/10.1007/s00190-006-0067-3 Huber argued that it is possible that the fluctuations of the green curve are entirely a stochastic artifact of the poor sampling afforded by the old eclipse records. Look carefully at the measured LOD and see that 100 years ago the earth was spinning slower than it is now, and slower than it was in 1972. The decadal fluctuations demonstrate that the torques caused by weather in the core/mantle boundary are huge by comparison to any geophysics beside impact with another planet. If another large decadal fluctuation slowdown happens there could be more than two leap seconds per year during this century. -- Steve Allen <sla@ucolick.org> 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 95064 http://www.ucolick.org/~sla/ Hgt +250 m