Ultima Thule

In ancient times the northernmost region of the habitable world - hence, any distant, unknown or mysterious land.

Tuesday, June 27, 2006

Scientists Precisely Track Short Term Earth Wobbles

By Aussiegirl

I had no idea that something as huge as the Earth could wobble. Here is an explanation I found for the Chandler wobble, discovered in 1891 by an American businessman turned astronomer: Writing in the August 1 [2000] 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.

Scientists Precisely Track Short Term Earth Wobbles

New technologies are enabling scientists to determine the extent and causes of Earth's short-term wobbling with extreme precision. Like a spinning top, Earth wobbles as it rotates on its axis. In fact, it displays many different wobbling motions, ranging in period from a few minutes to billions of years.

Some of these are well studied, such as the Chandler wobble of 433 days and the annual wobble, which together can tilt Earth's axis up to 10 meters (32 feet) from its nominal center.

Earth's irregular, shorter term wobbles, lasting a week or so, have been more difficult to study, partly because these motions are usually masked by those of more prominent wobbles.

Now, scientists in Belgium and France have taken advantage of a quirk in the pattern of large-scale motions and the advent of the Global Positioning System to pin down short-term wobbles that occurred from November 2005 through February 2006.

During this period, the Chandler wobble and the annual wobble essentially cancelled each other out, an event that occurs every 6.4 years, allowing the researchers to focus on the short-period wobbles. [....]

In a paper scheduled to be published 1 July in Geophysical Research Letters, they conclude that weather patterns in the northern hemisphere played a significant role.

Both the location of high- or low-pressure centers - for example, over Asia or northern Europe - and the relationship of these weather systems to each other played a measurable role in creating, or exciting, small, short-term wobbles, the team reported.

The ocean also affects short-term wobbles, according to Lambert and his colleagues. They were able to correlate oceanic and atmospheric pressure variations with the small observed wobbles during the study period.

Though these forces had been credited by previous researchers with maintaining the large Chandler wobble, this was the first time that scientists have been able to demonstrate that day-to-day changes in atmospheric pressure produce a measurable effect on Earth's rotation.


At 8:47 PM, Anonymous C.D. Economos said...

aussiegirl. I found you, better late than never. I'm not surprised there were no comments. When I observed the wobbles on home-made sundial-type equipment in 1998 and reported it on the Pacific Maritime Mobile Service Net (amateur radio), most fellows thought my crude equipment was being bumped. One sailor said it would explain why his sextant-read landfalls were a little hit-and- miss over the years. "I always thought it was my math," he said. It probably was his math. Of course, what I was observing was a course view of something easily denied. The modern GPS should clear all of this up. Today, just on a hunch, I searched the term 'short term earth wobble' and found your post. Thanks. my nickkname is Dino. I can't wait to do this experiment again. If it weren't for you, this could have been yet another 'message from the asylum.' w5dbg@yahoo.com


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