DIURNAL AND SEMIDIURNAL VARIATIONS IN THE EARTHS ROTATION RATE INDUCED BY OCEANIC TIDES

Recent space-geodetic observations have revealed daily and subdaily va riations in the Earth's rotation rate. Although spectral analysis sugg ests that the variations are primarily of tidal origin, comparisons to previous theoretical predictions based on various ocean models have b een less than satisfactory. This disagreement is partly caused by defi ciencies in physical modeling. Rotation predictions based on a reliabl e tidal-height model, with corresponding tidal currents inferred from a modified form of Laplace's momentum equations, yield predictions of tidal variations in Universal Time that agree with very long baseline interferometer observations to 2 microseconds. This agreement resolves a major discrepancy between theory and observation and establishes th e dominant role of oceanic tides for inducing variation in the Earth's rotation at these frequencies.