The ZMOA-1990 Nutation Series

Abstract

AbstractWe present a new nutation series for the Earth (ZMOA-1990) based on (1) the rigid Earth nutation series developed by Zhu and Groten [1989], (2) the normalized response for an elastic, elliptical Earth with fluid-outer and solid-inner cores developed by Mathews et al. [1990], and (3) corrections for the effects of ocean tides and anelasticity, computed to be consistent with the Mathews et al. [1990] normalized response function. In deriving this series, only two parameters of the geophysical model for the Earth have been modified from their values computed with PREM: the dynamic ellipticities of the whole Earth, e, and of the fluid outer core, ef. The adopted values for these parameters, determined from the analysts of very long baseline interferometry (VLSI) data, are e=0.00328915 which is about 1% higher than the value obtained from PREM and 6×10−5 times larger than the IAU adopted value, and ef=0.002665 which is 4.6% higher than the PREM value. The above values were obtained from an adjustment of −0.3 ʺ/cent to the IAU-1976 luni-solar precession constant for e, and from the amplitude of the retrograde annual nutation for ef. The ZMOA-1990 nutation series agrees with estimates of the in-phase and the out-of-phase nutation amplitudes obtained from VLBI data to within 0.5 mas for the terms with 18.6 year period, and to better than 0.1 mas for terms at all other periods except for the out-of-phase terms with annual period (differences 0.39 mas, retrograde, and 0.13 mas, prograde), and for the in-phase term with prograde 13.66 day period (difference −0.25 mas).