Replies to leapsecs. On Jun 19, 2008, at 1:33 PM, Marshall Eubanks wrote:
Leapseconds are driven by torques at the core mantle boundary, which we cannot see directly and basically have information about only through UT1 and LOD measurements. In practice, leap seconds cannot be predicted much more than 6 months to a year in advance because of that.
Modeling of Earth rotation has become exquisitely good. (Don't neglect information from seismology.) Discussions on LEAPSECS suggest that useful predictions are possible several years in advance. The horizon can be lengthened further by loosening the amplitude of DUT1 a skosh. A consensus appears likely around a set of parameters allowing for about a decade lookahead.
Note that the related science of helioseismology has progressed to the point that sunspots can be "seen" on the far side of the Sun. Hidden engines are studied quite productively throughout the sciences.
AND, keep in mind that in the "jerk" seen around 1905 would have meant several _negative_ leap seconds in one year, which would I am sure be a fun experience if repeated today.
We don't have leap seconds due to current variations, but due to integrating the already accumulated LOD offset of a few milliseconds. As the tidal offset grows quadratically, it has become virtually impossible for a negative leap second to occur, since such a jerk as you describe would have to persist long enough to overcome the accumulated temporal moment arm. The effective LOD zero point is in the nineteenth century, not the 1970's.
Rob Seaman NOAO _______________________________________________ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
