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    Re: no leap second coming in December
    From: George Huxtable
    Date: 2004 Jul 28, 00:28 +0100

    Thanks for information from Richard Langley and Andres Ruiz about this topic.
    
    Perhaps I can summarise the situation as follows-
    
    Right through most of the 20th century, up until 1994 or so, the difference
    between Ephemeris Time and Universal Time , or delta-T, increased each year
    by about 0.7 seconds. But over the last six years or so, this quantity has
    stopped increasing and at present remains roughly constant. This must be
    the result of the Earth's spin speed having increased, by about 1 part in
    40 million, rather suddenly, within a very few years.
    
    I know that delta-T has fluctuated significantly in the past, but this time
    there seems to have been a rather sudden increase in spin speed, by quite a
    large amount. What could be the cause of this rather dramatic change? One
    part in 40 million may not seem a lot at first sight, but in view of the
    immense angular momentum of the Earth, some large torques must have been at
    work.
    
    I would like to muse about some possibilities, aware that it's somewhat
    off-topic for navigation, but asking for a bit of indulgence on that score.
    
    It can't possibly be due to tidal friction, which causes angular momentum
    to be transferred from the Earth to the Moon, can it? That is strictly a
    one-way process, which can only ever act to slow the Earth's rotation, and
    never to speed it up.
    
    Could the Earth have shrunk slightly, perhaps? That would speed up the
    spin, as it does for an ice-skater doing a pirouette, as she draws in her
    outstretched arms. If the Earth radius were to shrink by one part in eighty
    million, with all its inner layers shrinking in proportion, that would be
    enough to do the trick. That needs no more than 3 inches or so shrinkage in
    radius. I suspect geodesists would be able to detect such an unlikely event
    using modern technology.
    
    It couldn't possibly be due to interaction with the moving atmosphere,
    which doesn't carry nearly enough mass to have sufficient effect.
    
    If the oceans were to acquire a change in East-to-West drift right around
    the Earth, including the Drake passage round the Horn, that would speed up
    the Earth's rotation, which is in the opposite direction. But to have
    sufficient effect, such a current drift would have to be sufficiently large
    that it would have been perceived already, according to my rough estimates.
    
    We keep getting told that the polar ice caps in Antarctica and Greenland
    are melting. However, this displacement of mass, from being locked in the
    ice caps near the Earth's axis, where it has little effect on the Earth's
    rotational inertia, to disperse around the oceans where its effect on
    inertia would be greater, could only slow the Earth's spin, not speed it
    up.
    
    The only other possibility that I'm aware of (and listed by Richard
    Langley) is a change in the circulating currents within the Earth's liquid
    interior. We know that these exist, and change, because these motions in
    the conductive liquid result in the ever-changing magnetic field pattern of
    the Earth. It seems most likely, to me, that there has been a significant
    increase over recent years, and a rather sudden one, in the component of
    overall swirl in the opposite direction to the rotation of the Earth. I
    wonder whether any such changes may be detectable in terms of a sudden
    effect on the Earth's magnetic field over recent years. It's just a
    thought.
    
    I admit to knowing little about geophysics, and hope that others, wiser
    about these matters, will correct any errors in my speculations.
    
    George.
    
    ================================================================
    contact George Huxtable by email at george@huxtable.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ================================================================
    
    
    

       
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