A New Free Core Nutation Model with Variable Amplitude and Period

TL;DR

This paper introduces a novel Free Core Nutation model with variable amplitude and period, improving the accuracy of celestial pole offset predictions by better matching VLBI observations.

Contribution

A new FCN model with variable amplitude and period is developed, enhancing the accuracy of nutation predictions compared to existing models.

Findings

Model shows better agreement with VLBI data.

Differences reduced to about 100 microarcseconds.

Variable period and amplitude improve fit.

Abstract

Three most long and dense VLBI nutation series obtained at the Goddard Space Flight Center, Institute of Applied Astronomy, and U.S. Naval Observatory were used for investigation of the Free Core Nutation (FCN) contribution to the celestial pole offset. Some recent studies have showed that the FCN period or/and phase does not remain constant, but varies in a rather wide range of about 410--490 days (for equivalent period). To implement this result in the practice, a new FCN model with variable amplitude and period (phase) is developed. Comparison of this model with observations shows better agreement than existing one. After correction of the differences between observed VLBI nutation series and the IAU2000A model, they decreased to a level about 100 microarcseconds.