Water: To Blame for Earth's Wobble

Water: To Blame for Earth's Wobble

The role of water in the universe never ceases to amaze. According to this NASA press release, water is responsible for the slight wobble of the Earth's axis of rotation:

A Mystery of Earth's Wobble Solved: It's In 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, California. 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 amplitude of 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.

Writing in the August 1 issue of Geophysical Research Letters, Richard S. Gross, of NASA's Jet Propulsion Laboratory, 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 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.

Gross credits the wide distribution of the data that underlay his calculations to the creation in 1988 of the International Earth Rotation Service (IERS), which is based in Paris, France. Through its various bureaus, he writes, IERS enables the kind of interdisciplinary research that led to his solution of the Chandler wobble mystery. Gross's research was supported by NASA's Office of Earth Science.

Media Relations Office, Jet Propulsion Laboratory
California Institute of Technology
National Aeronautics and Space Administration
http://www.jpl.nasa.gov
Contact:Rosemary Sullivant (818) 354-0474


Infinite Energy: Volume 6, issue 33, 2000 - Water special issue.

Polar melt, polar wobble?

As the northern pole ice melts, salinity in water is decreased, and ocean current motion will be destabilized, resulting in further polar wobble or shift.

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