HR: 0800h
AN: G41C-0369    [Abstracts]
TI: Outer Core Dynamics, Rotational Modes, and Tidal Deformation
AU: * Rogister, Y
EM: yves.rogister@eost.u-strasbg.fr
AF: Ecole et Observatoire des Sciences de la Terre, 5, rue Descartes, Strasbourg, 67000 France
AU: Valette, B
EM: Bernard.Valette@univ-savoie.fr
AF: LGIT, IRD, Université de Savoie, Le Bourget-du-Lac, 73376 France
AB: We have investigated the influence of the outer core structure on the Earth's rotational modes through the squared Brunt-Väisälä frequency N². The rotational mode frequencies are all imbedded into the continuous spectrum of inertia-gravity modes, which, in the complex domain, is governed by N² and the Earth's rotation speed. By solving the equations for the normal modes of a rotating ellipsoidal Earth and varying the N² parameter, we have shown bifurcations between core mode branches and the four rotational modes. For the FICN, a bifurcation results in two modes sharing similar displacements, i.e. an almost rigid wobble of the inner core and oscillations in the outer core. The corresponding eigenperiods in an inertial frame are separated by a few hundred days. The same kind of interaction occurs between core modes and the Chandler wobble of the mantle, the eigenperiods being now a few days apart in a co-rotating frame. The FCN shows much weaker interactions with core modes. Moreover, beside bifurcations similar to the ones for the FICN and Chandler wobble, the interactions between the FCN and core modes may be such that no mode exists for very narrow N² ranges. The fourth rotational mode is the Chandler wobble of the inner core. To date, its numerical computation still raises difficulties. We have been able to solve only the case N² = 0, which shows no interaction with core modes. A consequence of our results is that assuming a Poincaré motion in the outer core does not allow for a complete description of the interaction between the rotational modes and the core dynamics, especially for non-neutrally stratified models. Given that the core dynamics has possibly a significant influence on the motions of the mantle and inner core, we revisit the forced deformation of the rotating Earth. In particular, we investigate the diurnal and long-period tides. Because of the rotational coupling between displacements of different harmonic degrees, the long-period tides simultaneously involve degree 2 and degree 0 (purely radial) displacements. In this paper, we pay special attention to the long-period variations of J_2 that are associated to the degree 2 deformation.
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 1239 Earth rotation variations
SC: Geodesy [G]
MN: Fall Meeting 2005