Abstract:
This study addresses the challenge of enhancing the accuracy of Earth's polar motion modeling. Observational data indicate that variations in the parameters of the principal oscillatory modes (Chandler and annual wobbles) exhibit a component synchronous with the precession of the lunar orbit ($\sim 18.61$ years), which remains unaccounted for in standard models incorporating geophysical excitations. To incorporate this effect, a refined dynamic model is proposed and formulated as a system of differential equations with periodic coefficients dependent on the longitude of the Moon's ascending node.
Through numerical simulations based on International Earth Rotation and Reference Systems Service (IERS) data for the period 1976–2025, the optimal parameters of the model are determined: the lunar node coupling coefficient $\chi = 0.07$ and the quality factor $Q = 63$. The inclusion of the long-period lunar forcing is shown to reduce the standard deviation of the model from the observations. In test simulations, the accuracy in determining the pole position improves by an amount corresponding to 3.7 cm on the Earth's surface, with a maximum achievable improvement of up to 5 cm.
These results substantiate the necessity of explicitly incorporating long-period variations linked to the lunar orbit into high-precision models of polar motion.
Keywords:polar motion, lunar precession, differential equations, Chandler wobble, longitude of the ascending node, modeling, IERS
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