Resonances in solid Earth tides from VLBI observations

Abstract

This work pertains to the area of exploratory research aimed at finding very fine features of the Earth's tidal deformations at the limit of the capabilities of present-day astrogeodetic observations. Based on an analysis of almost all the available VLBI observations performed within the framework of IVS (International VLBI Service) geodetic programs in 1980-2014, we have obtained the corrections to the theoretical values of complex and frequency-dependent tidal parameters (Love/Shida numbers) for the first time. Their frequency dependence arises from the resonances attributable to the retrograde free core nutation (RFCN). Our results largely confirm a high accuracy of the theory of Earth tides presented in the modern International astrogeodetic standard, the IERS Conventions (2010). However, statistically significant corrections have been found for some harmonics of the lunisolar tide-generating potential. For example, the correction to the real part of the Love number h for the wave K1 with a frequency of 1 cpsd has turned out to be Δh R = −0.0142 ± 0.0006, which may be indicative of a deeper resonance than that predicted by the theory in the region of diurnal tides.