HR: 11:50h
AN: G51C-07 INVITED     [PDF]
TI: Hydromagnetic Oscillations of the Earth's Core: Constraints on the Structure and Dynamics of the Core from Geodetic and Geomagnetic Observations
AU: * Buffett, B A
EM: buffett@geosci.uchicago.edu
AF: Department of Geophysical Sciences, The University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637 United States
AU: Mound, J
EM: jon@sphere.physics.utoronto.ca
AF: Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON M5S 1A7 Canada
AB: Numerical models of the geodynamo have been remarkably successful in reproducing features of the Earth's magnetic field at the surface. However, the internal workings of different models can be surprisingly different. Efforts to distinguish between these possibilities are hampered by a lack of relevant observations. The most useful sources of information include estimates of fluid flow at the surface of the core, variations in the length of day, and changes in the gravity field. Interpreting this information relies on models to relate the observations to physical processes in the core. We address the need for better models by developing a new theoretical framework based on methods commonly employed in normal-mode seismology. The underlying mathematical models describe hydromagnetic waves in the core (torsional oscillations) and the accompanying motion of the mantle and inner core. The coupled motion of the core and mantle can be decomposed into an infinite set of normal modes. The frequency and spatial form of the normal modes depend on the physical properties of the core (include the structure of the internal magnetic field), whereas the modal amplitudes are related to the excitation source. The orthogonality of the normal modes is used to define a Green's function for the response of the system to an excitation which is localized in space and time. The predicted response for a spatially distributed, time-dependent source is obtained by convolving the source with the Green's function. We give several representative examples and show how this approach can be used to jointly invert observations of fluid flow at the core surface, variations in the length of day, and changes in the gravity field for the structure of the internal magnetic field and for the convective processes in the core that excite the oscillations
DE: 1212 Earth's interior--composition and state (8105)
DE: 1213 Earth's interior--dynamics (8115, 8120)
DE: 1239 Rotational variations
SC: Geodesy [G]
MN: 2003 Fall Meeting