Preliminary tide gauge evidence for equilibrium and non-equilibrium pole tide variability after the 2015 Chandler Wobble amplitude reduction

Abstract The pole tide has been defined as the oceanic response to polar motion, with a component due to the Chandler Wobble (CW), at a period near 14 months. The magnitude of the CW was greatly reduced after about 2015, and a corresponding global attenuation of the ocean pole tide amplitude is expected. We analyzed global tide gauge measurements using empirical orthogonal functions (EOF) methods to separate temporal and spatial patterns of regional pole tide signals. Our results show that tide gauge arrays in Japan and along the east coast of North America exhibit 14-month pole tide signals whose temporal variability is broadly consistent with the CW amplitude reduction after 2015. At stations in both regions, EOF-based mean pole tide amplitudes since 1980 fall in the range of approximately 0.5–1 cm, representing a more coherent signal than direct spectral estimates from individual stations. These amplitudes exceed the expected equilibrium response (less than 0.5 cm), suggesting that they reflect a mixture of equilibrium and moderate non-equilibrium contributions. Tide gauges in the North Sea and Baltic Sea show no detectable amplitude decrease after ~ 2015, consistent with previous studies documenting strong non-equilibrium pole tide variability in these regions. Together with the partial agreement with equilibrium expectations in Japan and along the North American east coast, these results suggest that regional pole tide signals likely reflect a combination of equilibrium response and additional forcing, potentially including long-period atmospheric variability. Graphical abstract