Forced nutations of the Earth: influence of inner core dynamics 3. Very long interferometry data analysis

Abstract

We discuss the analysis of 798 very long baseline interferometry (VLBI) experiments carded out between July 1980 and February 1989, and the determination from this analysis of corrections to selected coefficients in the International Astronomical Union (IAU) 1980 theory of the nutations of the Earth. Our analysis confirms earlier VLBI results and indicates that most of these corrections can be explained by carefully accounting for (1) corrections to the IAU 1980 rigid-Earth nutation series, (2)the presence of the Earth's inner core, (3) the difference between the dynamic flattening of the Earth inferred from the precession constant and that inferred from seismic models of the internal density structure of the Earth, and (4) the effects of mantle anelasticity and ocean tides. The standard deviations of the corrections to the coefficients are 0.04 milliarcseconds (mas) for terms with periods under 430 days, and 1.0 mas for the terms with a period of 18.6 years. The unresolved issues raised by our analysis are the origins of corrections to the out-of-phase retrograde annual(0.39 mas) and the in-phase prograde 13.66 day (- 0.25 mas) nutations. Our analysis also yields a correction to the IAU 1976 value for the luni-solar precession constant of -0.32±0.13 arc sec/century (cy).