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In this study, we use a nonlinear and non-stationary time series analysismethod, the ensemble empirical mode decomposition method (EEMD), to analyzethe polar motion (PM) time series (EOP C04 series from 1962 to 2013) to finda 531-day-period wobble (531 dW) signal. The 531 dW signal has been foundin the early PM series (1962–1977), but cannot be found in the recent PMseries (1978–2013) using conventional analysis approaches. By virtue of thedemodulation feature of EEMD, the 531 dW can be confirmed to be present inPM based on the differences of the amplitudes and phases between differentintrinsic mode functions. Results from three sub-series divided from the EOPC04 series show that the period of the 531 dW is subject to variations, inthe 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 the531 dW can only be observed in recent 30-year PM time series after usingEEMD. The 531 dW is also detected in the two longest availablesuperconducting gravimeter (SG) records, which further confirms the presenceof the 531 dW. The confirmation of the 531 dW existence could besignificant in establishing a more reasonable Earth rotation model and mayeffectively contribute to the prediction of the PM and its mechanisminterpretation

Search for the 531-day-period wobble signal in the polar motion based on EEMD