[G04-2] Earth rotation and geodynamics II

[G04-2-06] Empirical approach to the consistency and accuracy of the current IAU 2006/2000A precession-nutation model

Santiago Belda^{1, 2}, ^○Jose M. Ferrandiz¹, Robert Heinkelmman², Maria Karbon², Tobias Nilsson², Harald Schuh² (1.University of Alicante, Alicante, Spain, 2.GFZ German Research Centre for Geosciences, Potsdam, Germany)

Due to the gravitational attractions from the Moon, Sun, and planets, the Earth rotation axis shows various periodical motions w.r.t its figure axis. The forced nutations can be precisely modelled and predicted using the IAU 2006/2000A precession-nutation model which relates the International Celestial Reference Frame (ICRF) to the International Terrestrial Reference Frame (ITRF). Currently IAU 2000A/20006 only contains the easiest to predict astronomically forced terms, and thus, the Free Core Nutation (FCN), caused by the fluid outer core and the exchange of angular momentum among the Earth's components, is not included. It causes deficiencies in the IAU 2006/2000A precession-nutation model up to the order of 0.2 mas.
In order to empirically evaluate the consistency and deviations of the aforementioned model we computed several time series of Celestial Pole offsets (CPO) derived from the global analysis of the VLBI sessions since 1990 with varied settings to reflect the impact on the CPO estimates. These series were used to recalculate and adjust the precession constant offset and rate, as well as the main nutation amplitudes of the IAU 2006/2000A precession-nutation model, trying to empirically improve and update the conventional values adopted by the International Astronomical Union (IAU) and the International Association of Geodesy (IAG) and used by the International Earth Rotation and Reference Systems Service (IERS) Conventions 2010. Amplitudes of the FCN were also included in the previous adjustment and compared with other empirical FCN models.