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

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. 1 Known empirical FCN models To date, three empirical FCN models have been developed: MHB2000 [1], Malkin (ZM) [2], Lambert (SL) [3]. Comparison of these models with results of VLBI observations shows that all three models allow one to account equally essentially for the FCN contribution. However, as can be seen from fig. 1, ZM model provides smooth and, apparently, more realistic representation of variations of the basic geophysical parameters, the FCN amplitude and phase. It should be noted, however, that all models only approximate the observed variations in the celestial pole offset, without striking into the FCN physical properties. Further development of FCN model can be reached by consideration of a two-frequency FCN theory. Presented at the EGU 4th General Assembly, Vienna, Austria, 15-20 April 2007 1 0 0.1 0.2 0.3 0.4 0.5 1985 199