Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd..16e..52c&link_type=abstract
Nomenclature, Precession and New Models in Fundamental Astronomy, 26th meeting of the IAU, Joint Discussion 16, 22-23 August 200
Astronomy and Astrophysics
Astronomy
Scientific paper
The IAU 2000A Precession-Nutation Model includes parameters, which take into account various properties of the nonrigid Earth - mantle anelasticity, ocean tides, electromagnetic couplings between the fluid outer core and mantle and between the inner core and outer core with consideration of nonlinear terms. This model is based on trigonometric approximation of the nutation oscillations with use of five Fundamental Arguments (Delaunay variables) and linear amplitude changes. The nutation series consist of 678 lunisolar terms and 687 planetary terms, represented by several thousands coefficients. The direct determination and improving of all coefficients from observation is impossible, because many of the oscillations are with close frequencies and corresponding beating periods are greater than the existing observational time spans. Here the possibilities of decreasing the number of nutation terms without accuracy loss are investigated. The nutation variations according the Precession-Nutation Model IAU 2000A are separated into three frequency bands, corresponding to the 18.6-year oscillations, annual oscillations and high-frequency part with periods below 30 days. The variations of the amplitudes and phases of the 18.6-year and annual oscillations and their harmonics are determined in the running windows. The variations of the parameters of the high-frequency part are determined for several combinations of the Moon periods in the running windows with different sizes. This approach allows another point of view of the variations of the main nutation terms. The possibility for application of mixed polynomial and trigonometric approximations in the nutation theory are discussed.
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