Physics – Geophysics
Scientific paper
Jun 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991phdt........22b&link_type=abstract
Ph.D. Thesis Harvard Univ., Cambridge, MA.
Physics
Geophysics
Asphericity, Diurnal Variations, Elastic Deformation, Excitation, Geodynamics, Modes (Standing Waves), Nutation, Earth Tides, Ellipticity, Equations Of Motion, Geophysics, Ohmic Dissipation
Scientific paper
To explore the possible effects of inner and outer core dynamics on nutations, a simple model is developed consisting of a rigid mantle and inner core, and an adiabatic fluid outer core. The normal mode spectrum of this simple model reveals a number of modes that were not included in the International Astronomical Union (IAU) theory. Many of these modes are inertial waves, several of which have frequencies that fall within the tidal band and, therefore, are candidates for resonant excitation by nearby tidal forcing frequencies. The importance of inertial waves on nutations is shown to be comparable to a second class of modes that involve rotations of the solid inner core. The additional degrees of freedom associated with the rotation of an aspherical inner core give rise to two new modes that do not appear in the IAU theory. One is a prograde diurnal mode; the other is a long period inner core wobble. The second part of this thesis deals with physical processes that alter the nutations of the simple model considered above. The effects of elastic deformation are approached in a novel way by decomposing the equations of motion of a spheroidal and deformable model Earth into separate (though coupled) equations for the nutational and deformational parts of the motion. Results are used to compute the compliance parameters, which characterize the deformability of the Earth. In the first order calculation, corrections to the deformation are calculated for the omitted effects of ellipticity and rotation. The chief source of improvement between theory and observation is due to the elimination of a 0.39 mas discrepancy in the retrograde annual nutations. This out-of-phase correction is attributed to ohmic dissipation which necessarily accompanies the magnetic coupling.
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