Acta Geodaetica et Geophysica, vol.56, no.2, pp.231-261, 2021 (SCI-Expanded)
In this study, the amplitudes and Greenwich phase-lags of the principal semidiurnal tides and the diurnal tides of the ocean tide loading displacements (OTLD) were estimated at the worldwide distributed 37 Very Long Baseline Interferometry (VLBI) stations using 36 years of geodetic VLBI observations from 1984 to 2020. Then, the level of agreement was assessed between the OTLD observed by the VLBI space geodesy technique and those of the recent global ocean tide models (GOTM), among others TPXO9-Atlas (Egbert and Erofeeva 2002), FES2014b (Carrère et al. 2012, 2016) and GOT4.10c (Ray 2013). Finally, the long-term, i.e. over the last three decades, variations of the principal semidiurnal and diurnal tidal constituents of OTLD as observed by VLBI were investigated. The lunar only M2 tide radial phasor vector differences between the VLBI OTLD model and the GOTM are revealed as the largest among all the principal tides and the coordinate components. The root-mean-square misfits of the phasor vectors between the VLBI OTLD model and the GOTM are found as the largest for the radial components over the coastal sites at the lunar M2 (from 0.9 to 1.0 mm) and O1 tides (0.4–0.5 mm), the solar S2 tide (0.5–0.6 mm), and the luni-solar K1 tide (0.4–0.5 mm). The best agreement of the VLBI OTLD model is found with the GOT4.10c in tangential components and the TPXO9-Atlas in radial components. Long-term variations are detected in the semidiurnal and diurnal tidal coefficients, i.e. the amplitudes and the Greenwich phase-lags from the sequential solutions of the Kalman filter. These variations, resembling quasi-periodic oscillations, are more evident at the M2, K2, K1, and O1 tides and larger in amplitudes at the coastal stations in radial components. The radial amplitudes and phase-lags of the K1 and O1 tides vary for all stations up to about 1.2 mm and 12 degrees, respectively. The long-term, i.e. over the last three decades, variations of the principal semidiurnal and diurnal tides of OTLD are found as affected to a large extent by the long-term mean sea level rise or falls.