Acta Geodynamica et Geomaterialia

Title: PERIOD AND Q-FACTOR OF FREE CORE NUTATION BASED ON DIFFERENT GEOPHYSICAL EXCITATIONS AND VLBI SOLUTIONS
Authors: Vondrák Jan and Ron Cyril
DOI: 10.13168/AGG.2020.0015
Journal: Acta Geodynamica et Geomaterialia, Vol. 17, No. 2 (198), Prague 2020
Full Text: PDF file (1.5 MB)
Keywords: Rotation of the Earth, geophysical excitations, geomagnetic jerks, VLBI, celestial pole offsets, free core nutation
Abstract: Three variants of geophysical excitations and seven different VLBI solutions of celestial pole offsets (CPO) are used to determine period and Q-factor of Free Core Nutation (FCN). Brzeziński’s broad-band Liouville equations (Brzeziński, 1994) are numerically integrated to derive geophysical effects in nutation in time domain. Possible effect of geomagnetic jerks (GMJ) is also considered. Best-fitting values of FCN parameters are estimated by least-squares fit to observed CPO, corrected for the differences between the FCN parameters used in IAU 2000 model of nutation and newly estimated ones; MHB transfer function is used to compute these corrections. It is demonstrated that different VLBI solutions lead to FCN parameters that agree on the level of their formal uncertainties, but different models of geophysical excitations change the results more significantly. Using GMJ excitations always brings improvement of the fit between integrated and observed CPO. The obtained results show that the best fit is achieved when only GMJ excitations are used. Our conclusion is that GMJ are very probably more important for exciting FCN than the atmosphere and oceans. Empirical Sun-synchronous correction, introduced in the present IAU 2000 nutation model, cannot be explained by diurnal atmospheric tidal effects.