Mathematics – Logic
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.g12a1051s&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #G12A-1051
Mathematics
Logic
1239 Rotational Variations
Scientific paper
Mass redistributions on or within the Earth as a consequence of geophysical processes and gravitational interactions with celestial bodies influence the Earth's rotation on sub-daily to secular time scales. Rotational variations manifest in polar motion and changes in length-of-day. The effects of excitations are superposed by free oscillations of the Earth, i.e. the Chandler wobble and the free core nutation. To get insight into the rotational dynamics of the Earth a non-linear gyroscopic model has been developed. In contrast to most of the former approaches the numerical model dispenses with any explicit information concerning amplitude, phase, and period of free oscillations. Thus, the characteristics of the Earth's free nutation has to be reproduced the model solely from rheological and geometrical parameters. By regarding the rotational deformation of the Earth's body in the model, the period of the free nutation is lengthened from the Euler period (304 days), which would be the period of the free oscillation if the Earth was rigid, to the Chandler period of approximately 434 days. As the rotational deformation is a backcoupling mechanism of polar motion on the Earth's rotational dynamics it is assumed that both period and amplitude of the Chandler wobble are time-dependent when considering additional excitation, e.g., from atmospheric or oceanic mass redistributions. To study this effect, the gyro is forced by consistent atmospheric and oceanic excitations. These are derived from the global atmospheric ECHAM3-T21 general circulation model which is based on sea-surface temperature registrations and from the ocean model for circulation and tides OMCT. Mass redistributions in the Earth's body due to gravitational and loading deformations are calculated and additionally introduced into the model. Besides, external torques are considered which are exerted by Moon and Sun. For validation, the numerical results of the gyro are contrasted to the geodetically observed time series of polar motion and length-of-day variations which are published by the IERS.
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