HR: 1330h
AN: G22A-0302    [PDF]
TI: Torsional Oscillations and Mechanisms of Core-Mantle Angular Momentum Exchange
AU: * Mound, J
EM: jmound@physics.utoronto.ca
AF: Department of Physics, Univesity of Toronto, 60 Saint George Street, Toronto, ON M5S 1A7 Canada
AU: Buffett, B
EM: buffett@geosci.uchicago.edu
AF: Department of Geophysical Sciences, University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637 United States
AB: Motions in the fluid core, observable through variations in the magnetic field, are known to correlate with length-of-day changes on decadal timescales. However the physical mechanism that enables the angular momentum exchange remains uncertain. Proposed mechanisms include electromagnetic, topographic and gravitational couplings. We use a finite volume model of the core-mantle system to investigate each mechanism with respect to observed properties of the fluid motion. General observational constraints include fluid velocities on the order of 10 km/yr, wave-like oscillations with decadal periods and an associated length-of-day signal of several milliseconds. Angular momentum exchange between the core and mantle has also been proposed to explain length-of-day oscillations at interannual periods. We find that for reasonable values of core and mantle properties, electromagnetic coupling is too weak and too dissipative for the observed fluid velocities to produce the required torques on the mantle. Similarly, core-mantle boundary topography is likely too small to produce the required angular momentum exchange. Gravitational coupling between the mantle and inner core is the candidate mechanism that best reproduces the observed behaviour, provided that inner core viscosity is sufficiently large.
DE: 1213 Earth's interior--dynamics (8115, 8120)
DE: 1239 Rotational variations
DE: 1507 Core processes (8115)
DE: 7207 Core and mantle
SC: Geodesy [G]
MN: 2003 Fall Meeting