Lambert, S.B.: 2006, Atmospheric excitation of the Earth's free core nutation. A&A, 457, 717-720.
and Malkin, Z.: 2005, Detection of phase disturbances of free core nutation of the Earth and their concurrence with geomagnetic jerks.
The quasi-periodic variations of estimated period P and quality factor Q of Free Core Nutation keep within the limit of 429.8-430.5 solar days in case in the period, and 17000-22000 in case of the quality factor.
Roosbeek, F., Defraigne, P., Feissel, M., and Dehant, V.: 1999, The free core nutation period stays between 431 and 434 sidereal days.
and Ron, C.: 2006b, Resonance effects and possible excitation of Free Core Nutation. In: A.
We demonstrated that all VLBI solutions yield similarly varying values of estimated period P and quality factor Q of Free Core Nutation
. The agreement among different IVS analysis centers is very good, the differences do not exceed their formal uncertainties.
Here [e.sub.R] denotes the dynamical ellipticity of the rigid Earth used to compute the rigid solution, [N.sub.0], [Q.sub.j] are complex constants, and [s.sub.j] are four complex resonance frequencies corresponding to Chandler Wobble (CW, with terrestrial period of about 435 days), RFCN, with celestial period of about 430 days, Prograde Free Core Nutation (PFCN, with celestial period of about 1020 days) and Inner Core Wobble (ICW, with terrestrial period of about 2400 days) respectively.
In order to solve theoretically the rotation of non-rigid Earth model, Brzezinski (1994) proposed so called broad-band Liouville equations, that take into consideration two main resonances--Chandler wobble and Free core nutation. In celestial frame and complex notation it reads
Atmospheric pressure term with inverted barometer correction (a simple oceanic model), combined with wind effects is sufficiently large to excite the observed free core nutation. The numerical integration yields both amplitudes and phases of the free motion comparable to the observations, even in the interval almost 25 years long.
and Petrov, S.D.: 1999, Observational evidence of the free core nutation and its geophysical excitation.
Florsch, N., and Hinderer, J.: 2000, Bayesian estimation of the free core nutation parameters from the analysis of the precise tidal gravity data.