Specification of Q for Chandler Wobble Directly from Polar Motion Data

Former dynamical equations of Chandler wobble did not introduce damping attenuation index. Therefore, it says that Q of Chandler wobble can not be easily specified directly from polar motion data. A resonance excitation model is introduced, which provides the reason that CW amplitude reserves an adequate level. And later, the resonance excitation model is developed into a parameter resonance one. The parameter resonance model shows that CW amplitude oscillates high in long period. In this paper, Q of Chandler wobble is easily specified from IERS polar motion data using the developed resonance excitation model. But since in resonance excitation model the damping index is linear, Q of Chandler wobble specified from the data shows a little small.Then frequency modulation is introduced. The frequency and damping parameter in the resonance excitation equation become as time-dependent parameters. Parameter resonance model can provide a revision of visco-elasticity for computing Q. Then the mean value of Q is 63, which is increasing slowly at the rate of 0.8 every secular period. This result is very much identical with the theoretical Q result of 69 under visco-elastic PREM model. It shows that parameter resonance model is exactly appropriate with the visco-elastic theoretical model. The long time tendency of Chandler wobble is figured out. Frequency modulation can be seen and analyzed spectrally. Time series of attenuation index is provided and time series of Q shows a very stable result in the figure.