HR: 1340h
AN: GP33A-0914    [Abstracts]
TI: Precessionally-Driven Dynamo in a Spheroid
AU: * Roberts, P H
EM: roberts@math.ucla.edu
AF: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, 405 Hilgard Ave, Los Angeles, CA 90095, United States
AU: Wu, C
EM: ccwu@ucla.edu
AF: Institute of Geophysics and Planetary Physics, University of California, Los Angeles, 405 Hilgard Ave, Los Angeles, CA 90095, United States
AB: More than a half century ago, Bullard conjectured that the motions necessary to generate the Earth's magnetic field in the Earth's electrically-conducting fluid core might be driven by the luni-solar precession. All that has been unequivocally established in the intervening 55 years is that precession can in principle supply the geodynamo with abundant power. The question of whether the geodynamo can draw on this power is still unanswered, though it seems probable from the work of Tilgner [Physics Fluids 17 (3): Art. No. 034104, 2005] that it can do so. Two types of precession-driven flows may be distinguished: in spherical precession, the mantle transmits motion to the core by viscous coupling; in non-spherical precession, the oblateness of the core-mantle boundary creates core motion through pressure differences. Non-spherical precession is geophysically the more relevant and is being studied in a spheroid using a computer code for solving the time-dependent incompressible dissipative MHD equations with finite differences on overlapping grids. As in the study of Kerswell [Geophys. Astrophys. Fluid Dynamics, 72, 107-144, 1993], Poincaré's basic solution in a precessing spheroid is found to be linearly unstable. Furthermore, it is shown that the nonlinear evolution of the flow can lead to dynamo action. These results will be reported.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1510 Dynamo: theories and simulations
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting