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Showing posts with label Chandlers Wobble. Show all posts
Showing posts with label Chandlers Wobble. Show all posts
Thursday, September 24, 2009
Monday, September 14, 2009
Monday, August 31, 2009
TechnologyReview.com | Earth's Chandler Wobble Changed Dramatically in 2005
Monday, August 31, 2009
New analysis shows that the Chandler Wobble in the Earth's axis changed phase by 180 degrees in 2005. The question is why
If you travel to the Arctic and attempt to find the axis of the Earth's rotation, you'll notice something odd. The position of this axis on the Earth's surface moves with a period of about 7 years. This is the combined result of two effects. The one we're interested today is called the Chandler Wobble with a period of 433 days and discovered by the eponymous American astronomer in 1891.
The Chandler Wobble is reasonably well understood. Any spinning sphere that it is not entirely spherical should wobble in this way. However, on Earth, the wobble varies in amplitude from decade to decade, a motion that is thought to be the result of the changes in pressure at the bottom of the oceans caused by fluctuations in salinity, temperature and ocean circulation.
But there is also something mysterious about the Chandler Wobble. In 1920, it underwent a sudden phase change of 180 degrees. Nobody knows why.
Now a new analysis of data on the Earth's rotation going back 160 years indicates that this event was not unique. Zinovy Malkin and Natalia Miller at the Russian Academy of Sciences Central Astronomical Observatory in Pulkovo say that the phase has changed by small amounts on many occasions during this time. But the big news is that the Wobble underwent 180 degree changes in phase on two other occasions: once in 1850 and the other in 2005.
So why should the Chandler Wobble undergo these changes in phase? An interesting puzzle for anybody with a few brain cycles to spare.
Ref: arxiv.org/abs/0908.3732: Chandler Wobble: Two More Large Phase Jumps Revealed
Thursday, August 27, 2009
AccuWeather.com | Wobbling Earth and Climate Change
AccuWeather.com: Global Warming News, Science, Myths, ArticlesGlobal warming episodes that were interspersed between prehistoric ice ages were caused by regular wobbles in the earth's tilt, according to new evidence from the University of Newcastle in Australia. Image courtesy of Wikipedia. ...
Wednesday, August 12, 2009
Saturday, August 8, 2009
INTERNATIONAL EARTH ROTATION & REFERENCE SYSTEMS SERVICE
Chandler wobble
From Wikipedia, the free encyclopedia
The Chandler wobble is a small motion in the Earth's axis of rotation relative to the Earth's surface, which was discovered by American astronomer Seth Carlo Chandler in 1891. It amounts to 0.7 arcseconds (about 15 meters on the Earth's surface) and has a period of 433 days. This wobble combines with another wobble with a period of one year so that the total polar motion varies with a period of about 7 years. The Chandler wobble is an example of the kind of motion that can occur for a spinning object that is not a sphere; this is called a free nutation. Somewhat confusingly, the direction of the Earth's spin axis relative to the stars also varies with different periods, and these motions (caused by the tidal attraction of the Moon and Sun) are also called nutations, except for the slowest, which is the precession of the equinoxes.
The existence of a free nutation of the Earth was predicted by Leonhard Euler in 1755 as part of his studies of the dynamics of rotating bodies. Based on the known flattening of the Earth he predicted that it would have a period of 355 days. Several astronomers searched for motions with this period, but none were found. Chandler's contribution was to look for motions at any possible period; once the Chandler wobble was observed, the difference between its period and the one predicted by Euler was explained (by Simon Newcomb) as being caused by the non-rigidity of the Earth. The full explanation for the period also involves the fluid nature of the Earth's core and oceans: the wobble in fact produces a very small ocean tide, the pole tide, which is the only tide not caused by bodies outside the Earth.
To measure the wobble, the International Latitude Observatories were established in 1899. (The wobble is also called the variation of latitude). These provided data on the Chandler and annual wobble for most of the 20th century, though they were eventually superseded by other methods of measurement. Monitoring of the polar motion is now done by the International Earth Rotation Service.
The wobble's amplitude has varied since its discovery, reaching its largest size in 1910 and fluctuating noticeably from one decade to another. While it has to be maintained by changes in the mass distribution or angular momentum of the Earth's outer core, atmosphere, oceans, or crust (from earthquakes), for a long time the actual source was unclear, since no available motions seemed to be coherent with what was driving the wobble. On 18 July 2000, however, the Jet Propulsion Laboratory announced that "the principal cause of the Chandler wobble is fluctuating pressure on the bottom of the ocean, caused by temperature and salinity changes and wind-driven changes in the circulation of the oceans."[1]
[edit] Notes
- ^ A Mystery of Earth's Wobble Solved, Jet Propulsion Laboratory press release announcing cause of the Chandler wobble, July 18, 2000
References
- Carter, B, and M.S, Carter, 2003, "Latitude, How American Astronomers Solved the Mystery of Variation", Naval Institute Press, Annapolis.
- Lambeck, K., 1980, The Earth's Variable Rotation: Geophysical Causes and Consequences,
- Munk W. H. and MacDonald, G. J. F., 1960, The Rotation of the Earth, Cambridge University Press, London.
External links
- International Earth Rotation Service (IERS)
- The United States Naval Observatory - graph for 2005 and historical data
- Mystery of wobbly Earth solved, July 19, 2000
- Major Anomaly In Chandler's Wobble, Michael Mandeville
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