Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981cha%26a...5..460z&link_type=abstract
Chinese Astronomy and Astrophysics, Volume 5, Issue 4, p. 460-468.
Astronomy and Astrophysics
Astrophysics
1
Scientific paper
This paper introduces the idea that there exists a nutation separation layer in the superficial zone of the Earth, thereby sets up a new model of nutation. The equations of motion are derived and solved. It is proved that the separation layer is ``soft'', and is probably located at a depth of 300 km from the surface. Its allowable minimum thickness is less than 1 km and its viscosity is on the order of 1010 poise, like pitch at 15 °C. The results show that the main peak of the Chandler wobble (CW) is double, one being the nutational frequency of the inner main body, the other , the outer component. The beat between the two frequencies produces the 40-yr period in the amplitude of the CW. The two amplitudes interact so they do not differ greatly in size, their approximate ratio being 1 to 0.7. The famous amplitude-period relation of the CW is a direct result of this paper. The sudden changes in the polar trace and the 180° phase change in 1924-1926 are essentially the same phenomenon determined by relative changes in the two frequencies. The value of Q for the CW of between 30 and 60 deduced by previous workers from observations is a false Q, the true Q is around 200, in agreement with the value from seismic waves. This paper also predicts that apart from the two main frequencies, there is a series (more than one pair) of secondary frequencies symmetrically located on either side. The time constant of the CW is about 70 yr and it can be approximately maintained by excitation by earthquakes. Its unsmooth motion is one that zigzags about the mean trace.
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