On the double-peak spectrum of the Chandler wobble

Abstract

Abstract.It is well known that two close spectral peaks with comparable amplitudes exist in the Chandler wobble (CW) band in the observed polar motion spectrum during the first half of the past century. However, it is not generally accepted that the CW is an oscillation with two closely lying frequencies, and some authors attribute the appearance of these two peaks to some unusual phase variation (180• shift) of the CW during 1920s-1930s. In this note, the phase variation of the CW is explored using the longest Earth orientation parameter (EOP) time series currently available-the International Earth Rotation and Reference System Service (IERS) EOP-C01 from 1846 to 2003. The observation time series mainly containing the CW obtained by removing the annual wobble (AW) from the original EOP time series is compared with a synthetic double frequency CW times series constructed using the frequencies, amplitudes and initial phases of the two peaks precisely determined using spectral analysis. The result shows reasonable agreement between their peak times, a feature not shown before. This feature is in agreement with the hypothesis of a double frequency CW. While the result shown here is inconclusive that the CW really has two frequencies, this note is expected to serve as a reminder for its renewed interest.

On modulations of the Chandler wobble excitation

“…For the Chandler wobble to keep going, the energy associated with this motion should be replenished constantly and should have a stochastic part sufficient to cause the irregularities of this mode (Jeffreys, 1940). It was also proposed (see Guo et al, 2005) that the Chandler oscillation is a double frequency mode or that a widespread annual excitation causes its irregularities. We shall not consider this hypothesis here.…”

Dynamical Modeling and Excitation Reconstruction as Fundamental of Earth Rotation Prediction

“…For example, the double peak of Chandler wobble spectrum has been analysed whether it is one or two close by frequency oscillations. In the work of Guo et al (2005) this is discussed in detail and it's concluded, that we should wait until 2030-th, when, in case of dual components, Chandler oscillations should decrease, as in 1930-th. Though, as it can be seen from Figure 2b there is a tendency of Chandler component to decrease in the last decade, we still supposed in our study, that there is one resonance frequency, what can be physically derived from the theory of the Earth's rotation, as it was developed in works of Euler, Liouville, Poincare and others.…”

Amplitude and phase variations of Earth's Chandler wobble under continual excitation

“…Per the thought experiment above, this is the reason why the observed Chandler wobble appears to be amplitude-modulated and phase-modulated, which in effect explains why the observed Chandler wobble appears to be of multi-frequency (cf. Chao, 1983;Guo et al, 2005). Conversely, de-convolution of the observed Chandler wobble off its free motion reveals the excitation function.…”