Limitations of the IAU2000 nutation model accuracy due to the lack of Oppolzer terms of planetary origin

¹ Dept. of Applied Mathematics, University of Alicante, PO Box 99, 03080 Alicante, Spain
e-mail: jm.ferrandiz@ua.es
² Dept. of Aerospace Engineering, University of León, 24071 León, Spain
³ Dept. of Applied Mathematics, University of Valladolid, 47011 Valladolid, Spain

Received: 21 March 2017
Accepted: 4 July 2018

Abstract

Context. The current IAU2000 nutation model performed different approximations, one of them being that the Oppolzer terms associated to the planetary perturbations of the nutations were assumed to be smaller than 5 μas and thus were neglected. At present, the uncertainties of the amplitudes of individual components of the observed nutations are better, and the conventional nutation model does not fit the accuracy requirements pursued by the International Astronomical Union (IAU) and the International Association of Geodesy (IAG).

Aims. The objective of this work is to estimate the magnitude of the lacking Oppolzer terms of the planetary nutations and find out whether they are still negligible or not.

Methods. The Oppolzer terms resulting from the direct and indirect planetary perturbations of the Earth’s rotation have been computed for a two-layer Earth model following the Hamiltonian theory of the non-rigid-Earth.

Results. The planetary Oppolzer terms for the non-rigid Earth are not really negligible as believed, and some of them have amplitudes larger than 10 μas, therefore significantly above the current level of uncertainty of individual harmonic constituents.

Conclusions. In the short term, the IAU2000 nutation model must be supplemented with suitable corrections accounting for those missing components; its planetary component must be thoroughly revised in the medium term.