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Stroller
2009-Jul-25, 10:25 PM
Hi all, I want to find out about the astronomical aspects to the small changes that occur in the Earth's Length of Day (LOD). I read in an article on the NASA website (http://www.jpl.nasa.gov/news/features.cfm?feature=15) by Richard Gross that:



The longer patterns in changes of the length of the day can last for decades. "These are caused by processes within Earth's core," says Gross. "The core is a fluid. Its motion generates Earth's magnetic field. Changes in its motion can change the rotation of solid Earth. Observing the magnetic field at the surface gives us an idea of how fluid is moving within the core. These changes in the fluid motion inferred from the magnetic field match the longer period changes we see in the length of the day."


I wondered what external influences there might be that might affect the motion of the material in Earth's core and if there are any of a significant magnitude, whether they would be electromagnetic or gravitational.

I read in a paper by Laskar: Large scale chaos and the spacing of the inner planets, that the solar system's inner planets wouldn't be in quasi stable orbits unless their chaotic tendencies were bounded by angular momentum exchanges which prevent their orbits overlapping. (If I understood correctly!)

I also read in an abstract of a paper by two Chinese scientists who had performed a wavelet analysis that LOD correlates closely with the length of the solar cycle.

So can anyone tell me if LOD is affected by either or both angular momentum exchanges with other planets and electromagnetic effects associated with the solar cycle?

Thanks in advance for any answers or pointers.