LONG-PERIOD TIDES OBSERVED WITH A SUPERCONDUCTING GRAVIMETER AT SYOWASTATION, ANTARCTICA, AND THEIR IMPLICATION TO GLOBAL OCEAN TIDE MODELING

The long-period tides (Mf and Mm waves) were analyzed with the 2 years data obtained with a superconducting gravimeter (SG) installed at Syo wa Station (69.0 degrees S, 39.6 degrees E), Antarctica. The observed amplitudes, phase lags and amplitude factors (S factors) were 11.642 /- 0.035 mu Gal, -0.12 degrees +/- 0.17 degrees and 1.1218 +/- 0.0034 for the Mf wave, and 6.143 +/- 0.058 mu Gal, 0.33 degrees +/- 0.54 deg rees and 1.1205 +/- 0.0106 for the Mm wave, respectively (1 mu Gal = 1 0(-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 tid es. Geophys. J. Int. 99, 457-468.), CSR model (Eanes, R.J,, 1995. Priv ate communication.), and Desai and Wahr model (Desai, S.H., Wahr, J.M. , 1995. Empirical ocean tide models estimated from TOPEX/POSEIDON alti metry. J. Geophys. Res. 100, 25205-25228.). The averages of the five e stimates are 0.433 mu Gal and 0.244 mu Gal in amplitude and 192.9 degr ees and 179.5 degrees in phase for the Mf and Mm waves, respectively. The five estimates differ by a maximum of 0.104 mu Gal in amplitude an d 18.8 degrees in phase for the Mf wave, and by 0.033 mu Gal and 6.4 d egrees for the Mm wave. The estimated Mm phases are nearly 180 degrees for the five models, and the variation of their values among the mode ls is relatively small compared with that of the Mf phases. These indi cate that the Mm wave is much closer to an equilibrium tide than the M f wave. Due to the variation of the ocean tide corrections, the correc ted delta factors were scattered within the ranges of 1.158 to 1.169 f or the Mf wave and of 1.163 to 1.169 for the Mm wave. However, it is n oted that the mean delta 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 t he elastic tide. (C) 1997 Elsevier Science B.V.