Long-period tides observed with a superconducting gravimeter at Syowa Station, Antarctica, and their implication to global ocean tide modeling

Abstract

The long-period tides (Mf and Mm waves) were analyzed with the 2 years data obtained with a superconducting gravimeter (SG) installed at Syowa Station (69.0° S, 39.6° E), Antarctica. The observed amplitudes, phase lags and amplitude factors (δ factors) were 11.642 ± 0.035 μGal, −0.12° ± 0.17° and 1.1218 ± 0.0034 for the Mf wave, and 6.143 ± 0.058 μGal, 0.33° ± 0.54° and 1.1205 ± 0.0106 for the Mm wave, respectively (1 μGal = 10 −8 m s −2). The ocean tide effects (effects of the attraction and loading due to the ocean mass) at the observation site were estimated using the five global ocean tide models: equilibrium ocean tide model, Schwiderski model (Schwiderski, E.W., 1980. On charting global ocean tides. Rev. Geophys. Space Phys. 18, 243–268.), Dickman model (Dickman, S.R., 1989. A complete spherical harmonic approach to luni-solar tides. Geophys. J. Int. 99, 457–468.), CSR model (Eanes, R.J., 1995. Private communication.), and Desai and Wahr model (Desai, S.H., Wahr, J.M., 1995. Empirical ocean tide models estimated from TOPEX/POSEIDON altimetry. J. Geophys. Res. 100, 25205–25228.). The averages of the five estimates are 0.433 μGal and 0.244 μGal in amplitude and 192.9° and 179.5° in phase for the Mf and Mm waves, respectively. The five estimates differ by a maximum of 0.104 μGal in amplitude and 18.8° in phase for the Mf wave, and by 0.033 μGal and 6.4° for the Mm wave. The estimated Mm phases are nearly 180° for the five models, and the variation of their values among the models is relatively small compared with that of the Mf phases. These indicate that the Mm wave is much closer to an equilibrium tide than the Mf wave. Due to the variation of the ocean tide corrections, the corrected δ factors were scattered within the ranges of 1.158 to 1.169 for the Mf wave and of 1.163 to 1.169 for the Mm wave. However, it is noted that the mean δ factors of the five ocean models, i.e. 1.162 ± 0.023 for the Mf wave and 1.165 ± 0.014 for the Mm wave, prefer slightly larger value rather than those estimated from the theory of the elastic tide.