The Contribution of a Newly Unraveled 64 Years Common Oscillation on the Estimate of Present‐Day Global Mean Sea Level Rise
2021
Ding, Hao | Jin, TaoYong | Li, Jiancheng | Jiang, Weiping
The multidecadal fluctuations in sea level changes play an important role in the exact quantification of present‐day global mean sea level (GMSL) rise and its acceleration. Here, we use an array processing technique (optimal sequence estimation) to analyze 44 global tide gauge (TG) sea‐level records with identical January 1933–December 2019 data spans. The results reveal for the first time a common 64.0 ± 3 years periodic oscillation with a spherical harmonic Y₂₁ spatial pattern. Based on the estimated equivalent “excitation” amplitude (A = 47.7 ± 2 mm) and phase (φ = −0.406 rad), we constructed a global model for this 64 years sea‐level fluctuation. The complex amplitudes of the extracted ∼64 years fluctuation from 94 TG records with different data spans, and of two GMSL time series are consistent with the corresponding results predicted by the constructed model using the stacking results using 44 TGs. We find that the 64 years oscillation has significant contributions on the estimate of reconstructed GMSL trend: it contributed about 24% to the sea‐level trend during 1993–2014 and cause a relative deceleration during 2024–2055; while it contributes slightly to the satellite‐based GMSL trend estimates during 1993–2020. We confirm that this 64 years signal is not originated from the Earth's polar motion; however, it has good consistency with the Earth's magnetic field dipole changes, and with the ∼65 years oscillation in the ΔLOD, which suggests that this 64 years signal could come from core motions. We believe our results unravel a new understanding of the mechanisms of GMSL's long‐term fluctuations within the Earth system.
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