Variable Chandler and Annual Wobbles in Earth’s Polar Motion During 1900–2015

Abstract

The Chandler wobble (CW) and annual wobble (AW) are the two main components of polar motion, which are difficult to separate because of their very close periods. In the light of Fourier dictionary and basis pursuit method, a Fourier basis pursuit (FBP) spectrum is developed, which can reduce spectral smearing and leakage caused by the finite length of the time series. Further, a band-pass filtering method based on FBP spectrum (FBPBPF), which can effectively suppress the edge effect, is proposed in this paper. The simulation test results show that the FBPBPF method can effectively suppress the edge effect caused by spectral smearing and leakage and that its reconstruction accuracy at the boundary is approximately three times higher than the Fourier transform band-pass filtering method, which is based on Hamming windowed FFT spectrum, in extracting quasi-harmonic signals. The FBPBPF method is then applied to Earth's polar motion data during 1900-2015. Through analyzing the amplitude and period variations of CW and AW, and calculating the eccentricity variation of the AW, we found that: (1) the amplitude of the CW is currently at a historic minimum level, and it is even possible to diminish further until a complete stop; and (2) the eccentricity of the AW has a gradually decreased fluctuation during the last 116 years.

The First-time Absence of the Chandler Wobble since 2015 and its Implications for Excitation Processes

“…Moreover, we show that the available Atmospheric Angular Momentum (AAM) and Oceanic Angular Momentum (OAM) cannot reproduce the recent CW anomaly. The decreasing trend of the CW amplitude has been already pointed out by some studies (e.g., Wang et al 2016;Malkin and Miller 2010), but it was unclear when the amplitude of CW became almost zero. In addition, no previous studies have examined the impact of AAM/OAM to check if they can account for the recent decrease in CW amplitude.…”

Continental and oceanic AAM contributions to Chandler Wobble with the amplitude attenuation from 2012 to 2022

“…Previous investigations have identified anomalies of the CW in the 2010s, with changes in atmospheric excitation suggested to be the likely reason (Wang et al 2016;Zotov et al 2022;Malkin 2023;Yamaguchi and Furuya 2024). In this study, we explored deeper into the factors contributing to the reduction in the CW amplitude.…”

The numerical prediction of the Earth’s polar motion based on an advanced multivariate algorithm

“…( 14), the a A and m A are the constants of the annual linear amplitude (Shen et al, 2018), f A = 1/365.25 is the annual frequency, and w A is the un-estimated phase. Instead of the assumption of an initial constant period (e. g., 428 days) in the biaxial rigid Earth (Becker, 1954), the later double-periods motion (e.g., 428 and 438 days) with the beat model (Colombo and Shapiro, 1968) or the recent variable period (e.g., from 392 to 441 days) under the sustained excitation (Wang G. et al, 2016), the MH fitting for CW was postulated as 5-period channels (namely, M = 5, Pan. 2007;Zhang et al, 1986) of T main {432 days}, T 1,0 and T 1,1 {symmetrical peaks: 429 and 435 days}, and T 2,0 and T 2,1 {symmetrical peaks: 406 and 447 days}.…”

“…Such Chandler frequency splits respond to the coupled oscillators in the triaxial or axially near-symmetrical Earth and are indeed equivalent to amplitude or frequency modulation (Pan, 2012). In routine practice, the CW was generally considered to have a fixed or time-varying frequency; for high-precision prediction, however, such choices may also introduce deviations (Malkin and Miller 2010;Wang G. et al, 2016). Akyilmaz et al (2011) further showed that the quasi-periodic and irregular processes in the PM residual need to be settled for prediction.…”