Inversion of polar motion data: Chandler wobble, phase jumps, and geomagnetic jerks

Abstract

We reconsider the analysis of the polar motion with a method totally different from the wavelet analysis used in previous papers. The total polar motion is represented as the sum of oscillating annual and Chandler terms whose amplitude and phase perturbations are inverted with a nonlinear simulated annealing method. The phase variations found in previous papers are confirmed with the huge phase change (≈3π/2) occurring in the 1926–1942 period and another less important one (≈π/3) in the 1970–1980 epoch. The best Chandler period, Tc, is found to be 434 ± 0.5 mean solar days. The epochs of significant phase changes found in the Chandler wobble are also those where important geomagnetic jerks occur in the secular variation of the geomagnetic field. Turbulent viscous friction produced by small‐scale topography at the core‐mantle boundary might be responsible for the observed phase jumps.

Geomagnetic Jerks: Rapid Core Field Variations and Core Dynamics

“…Both studies showed that these phase jumps appear to be correlated with geomagnetic jerks, and that geomagnetic jerks are followed by phase jumps in the Chandler wobble within at most 3.5 years. These first results have been more recently confirmed (Gibert et al 2008) using different techniques. In this new study, the total polar motion (the combination of the oscillating annual and Chandler terms) amplitude and phase perturbations are inverted with a nonlinear simulated annealing method.…”

“…In this new study, the total polar motion (the combination of the oscillating annual and Chandler terms) amplitude and phase perturbations are inverted with a nonlinear simulated annealing method. Both studies (Gibert et al 1998(Gibert et al , 2008 indicate that a large phase change of around 180 • occurs in the decade after 1926 and another phase change, also remarkable, in the decade after 1970. This last event can be observed in Fig.…”

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

“…Thus, we do not subscribe to the view that something extraordinary or anomalous had occurred to the Earth system during the 1920s as far as the Chandler phase reversal is concerned (as suspected in, e.g., Bellanger et al, 2002;Gibert and Le Mouël, 2008;Vondrak and Ron, 2005;Malkin and Miller, 2010). The said Chandler phase jump was simply a consequence of the fortuitous small Chandler amplitude at the time; such episodes would occur by chance from time to time, which not surprisingly indeed occurred once during the ∼1 century of observation, a time span comparable to the Q timescale of Chandler wobble.…”

Dynamical Modeling and Excitation Reconstruction as Fundamental of Earth Rotation Prediction

“…It helps to judge about the temporal and frequency resolution of corrective smoothing and of Gabor transform used in our work. Gibert and Le Mouel (2008), almost disappears in excitation. This can be explained by the inuence of the dynamical system (1), which introduces π phase shift (see Figure 4b).…”