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earth's wobble global warming ocean salinity

Posted by Jai Narayan on December 31, 2004, at 8:39:40

A MYSTERY OF EARTH'S WOBBLE SOLVED: IT'S THE OCEAN
The century-old mystery of Earth's "Chandler wobble" has been solved by a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. The Chandler wobble, named for its 1891 discoverer, Seth Carlo Chandler, Jr., an American businessman turned astronomer, is one of several wobbling motions exhibited by Earth as it rotates on its axis, much as a top wobbles as it spins.
Scientists have been particularly intrigued by the Chandler wobble, since its cause has remained a mystery even though it has been under observation for over a century. Its period is only around 433 days, or just 1.2 years, meaning that it takes that amount of time to complete one wobble. The wobble amounts to about 20 feet at the North Pole. It has been calculated that the Chandler wobble would be damped down, or reduced to zero, in just 68 years, unless some force were constantly acting to reinvigorate it.

       But what is that force, or excitation mechanism? Over the years, various hypotheses have been put forward, such as atmospheric phenomena, continental water storage (changes in snow cover, river runoff, lake levels, or reservoir capacities), interaction at the boundary of Earth's core and its surrounding mantle, and earthquakes.

From Wikipedia, the free encyclopedia.

       Writing in the August 1 issue of Geophysical Research Letters, Richard Gross, a JPL geophysicist, reports 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. He determined this by applying numerical models of the oceans, which have only recently become available through the work of other researchers, to data on the Chandler wobble obtained during the years 1985-1995. Gross calculated that two-thirds of the Chandler wobble is caused by ocean-bottom pressure changes and the remaining one-third by fluctuations in atmospheric pressure. He says that the effect of atmospheric winds and ocean currents on the wobble was minor.


The Chandler wobble is a small variation in Earth's axis of rotation, discovered by American astronomer Seth Carlo Chandler in 1891. It amounts to 0.7 arcseconds over a period of 435 days. In other words, Earth's poles move in an irregular circle of 3 to 15 metres in diameter, in an oscillation.

The wobble's diameter has varied since discovery, reaching its most extreme range recorded to date in 1910. The cause is unknown: barring any external force, the wobble should have eventually subsided. Originally it was believed that the wobble was caused by weather fluctuations from season to season causing shifts in atmospheric mass distribution, or possible geophysical movement beneath Earth's crust. 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."
The Chandler wobble is a factor considered by satellite navigation systems (especially military systems). It is also theorised as the cause of major tectonic activity, including earthquakes, volcanism, El Niņo, and global warming phenomenon.


Jai Narayan as we wobble into the new year 2005!
Happy New Year everybody


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poster:Jai Narayan thread:435962
URL: http://www.dr-bob.org/babble/social/20041226/msgs/435962.html