Analysis of Earth’s polar motion and length of day trends in comparison with estimates using second degree stokes coefficients from satellite gravimetry
We analyzed the impacts of data span on trend estimates using Earth’s long-term polar motion time series, 1846-present, and using methodologies including singular spectrum analysis, and Panteleev’s filter to mitigate the time series containing transient signals. Our results show that the fluctuations of the mean rotational pole position, the Markowitz wobble, cannot be fully explained by the oceanic and atmospheric excitations. However, there exists plausible similarity with the variations of amplitudes of the Chandler wobble. To explain the abrupt deviation of the mean pole from the previous state after year 2000, we first compute Earth rotation excitations, using the temporal variations of the second-degree Stokes coefficients, , estimated from GRACE, GRACE Follow-On and Satellite Laser Ranging (SLR), 2002–2021. We then compare their trend estimates with that of the Earth’s polar motion, and conclude that the drift of the pole is consistent with the climate-induced mass redistributions within the Earth system during the past two decades. However, the observed trend is not in exact agreement with the prediction values using contemporary glacial isostatic adjustment (GIA) process forward models. The analysis of the variations since 1976 from SLR and the corresponding length of day (LOD) changes, reveals a clear trend reversal around the year 2000. However, the observed variations can only explain of the long-term LOD changes. The remaining decadal signal in the LOD, usually accounted for by the angular momentum exchange at the core-mantle boundary, is observed to be anti-correlated with the Earth surface temperature anomaly. The geophysical explanation on these relationships remains elusive, and necessitates future studies.