Our Wobbling Earth, Wobbled by The World's Weather
By: Mark Boardman
As it rotates, the World wobbles as it spins on its axis. And as it slows down, the earth develops a host of different wobbles, ranging in time period from a few minutes to billions of years.
The confusion of why the position of the planet's poles wobbles by 7 meters has been solved by a NASA scientist. The wobble, which has a 433-day cycle, was discovered by the astronomer Seth Chandler in 1891 but no one could explain it. This is now known, quite rightly, as the Chandler wobble.
It would appear that changes in the ocean pressure on the Globe's crust are causing the wobble. The Earth vibrates at certain resonant frequencies. Small shifts in sea circulation, caused by changes in winds and sea salinity, affect the water pressure on the crust. This pressure change in turn alters one of the Earth's natural vibration frequencies, causing the wobble.
There is also an annual wobble caused by the pull of the Sun and Moon as the Earth spins around the Sun through the year, tilted at an angle of 23.5 degrees on the Earth's axis of rotation. The daily rotation of the globe creates a bulge at the equator, and the gravity of the Sun and Moon tends to pull this bulge back toward the orbital plane.
Even so the Globe tends to oppose this pull as it hurtles around it's orbit. For that reason the axis shifts in a cone-shaped pattern, called a precession, with the celestial North Pole completing a full circle every 26,000 years roughly. At this moment in time the north celestial pole is pointing towards Polaris, the North Star, but it used to point to Vega, and in 14,000 years it will point at Vega once again. During this time the Globe's tilt remains at 23.5 degrees.
These two wobbles together can tilt the Earth's axis up to 30 feet from its appropriate axis.
Even so , smaller variations, lasting seven days or so, have proved more difficult to study, partly because they're hidden by the more conspicuous wobbles. Now scientists say changes in the weather cause small wobbles in the entire planet's spin. From November 2005 until February 2006, the Chandler and annual wobbles pretty much cancelled each other out. This allowed scientists to study the minor variations. Using GPS data to establish the exact location of the poles, these skillful boffins determined that world weather patterns play a significant role in the small wobbles.
The location of cyclonic and anti-cyclonic centres and the relation of these high and low pressure systems to each other played a measurable role in producing small wobbles. These systems caused the pole positions to swing in small loops ranging from a couple of centimetres to several inches. The study also proved that sea pressure variations also coincided with these small polar loops.
So it would appear that day to day changes in the whole world's weather has a small, but definite and measurable, effect on the Earth's rotation.
Mark Boardman BSc dip.hyp is a leading author and expert on world weather. For more information about our planets weather, go and look at these sites. Mark's Hypnosis Site.
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