An analysis of celestial pole offset observations in the free core nutation frequency band

TL;DR

This paper compares empirical models of free core nutation, finds the most realistic one, and provides evidence for two close FCN periods in Earth's rotation, supported by VLBI data and theoretical explanations.

Contribution

It introduces a detailed analysis of FCN models and presents evidence for dual FCN periods, enhancing understanding of Earth's rotational dynamics.

Findings

The MHB2000 model best represents FCN variations.

VLBI data indicates two close FCN periods around 452 and 410 days.

Theoretical explanation supports the presence of two FCN frequencies.

Abstract

In this study, three empirical Free Core Nutation (FCN) models developed to the present time, MHB2000, Malkin's and Lambert's ones, are compared on the basis of representation of variations of the FCN amplitude and phase predicted by these models. It is possible to conclude, that the model of the author provides the most realistic representation of the FCN variations. However, the specified models are based on representation about single FCN rotational mode. At the same time, some results of processing of the VLBI observations made during last years, specify possible presence of two close FCN periods. A theoretical explanation to presence of a second FCN frequency FCN has been given by G. Krasinsky in his theory of rotation of the Earth with two-layer liquid core, ERA2005. In the present work, for more detailed studying this phenomenon, the IVS time series of celestial pole offset, and also those predicted by the ERA2005 theory, have been investigated by means of several statistical methods which confidently show presence of two fluctuations in nutational movement of an Earth's rotation axis with the periods about -452 and -410 solar days.