Abstract
Abstract. In this study, we use a nonlinear and non-stationary time series analysis method, the ensemble empirical mode decomposition method (EEMD), to analyze the polar motion (PM) time series (EOP C04 series from 1962 to 2013) to find a 531-day-period wobble (531 dW) signal. The 531 dW signal has been found in the early PM series (1962–1977), but cannot be found in the recent PM series (1978–2013) using conventional analysis approaches. By virtue of the demodulation feature of EEMD, the 531 dW can be confirmed to be present in PM based on the differences of the amplitudes and phases between different intrinsic mode functions. Results from three sub-series divided from the EOP C04 series show that the period of the 531 dW is subject to variations, in the range of 530.9–524 days, and its amplitude is also time-dependent (about 2–11 mas). Synthetic tests are carried out to explain why the 531 dW can only be observed in recent 30-year PM time series after using EEMD. The 531 dW is also detected in the two longest available superconducting gravimeter (SG) records, which further confirms the presence of the 531 dW. The confirmation of the 531 dW existence could be significant in establishing a more reasonable Earth rotation model and may effectively contribute to the prediction of the PM and its mechanism interpretation.
Highlights
It is recognized that the polar motion (PM) contains two dominant components: the annual wobble (AW) with a 12month period and the Chandler wobble (CW) with a 14month period
The waveforms of the two components, the x- and ycomponents of the chosen PM series are shown in Fig. 1a, and their corresponding Fourier spectra are shown in Fig. 1b, c
Given that the empirical mode decomposition method (EEMD) is based on the waveform of the time series to filter different signals for different intrinsic mode functions (IMFs), we have confirmed that the distinction at 1980 will not significantly affect our results
Summary
It is recognized that the polar motion (PM) contains two dominant components: the annual wobble (AW) with a 12month period and the Chandler wobble (CW) with a 14month period. The first upper and lower sidebands could be at 1 cpy (cycles per year) and 0.69 cpy, respectively, when the beat frequency is 0.157 cpy (CW’s frequency 0.843 cpy ± k × 0.157; k = 1 denotes the first upper and lower sidebands), where the beat frequency or beat period is the time period required for the Earth’s pole to complete a cycle of the combined AW (12 months) and CW (14 months). Based on a 16-year time series of International Polar Motion Data (spanning from 1962 to 1977), a 0.686 cpy component with its amplitude being around 10 to 17 mas (milliarcsecond) was very weakly detected in Carter (1982), but its signal-to-noise ratio (SNR) is very low.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
