HR: 17:30h
AN: GP44A-07 INVITED     [Abstracts]
TI: Locking of the Magnetic Field Onto the Lower Mantle.
AU: * Gubbins, D
EM: gubbins@earth.leeds.ac.uk
AF: School of Earth and Environment, University of Leeds, Leeds, LS29JT United Kingdom
AB: The present geomagnetic field at the core surface exhibits a striking symmetrical pattern of 4 flux lobes situated just outside the tangent cylinder. They may arise from concentration of flux by downwelling in the core induced by cold regions in the lower mantle boundary layer. Numerical experiments of non-magnetic rotating convection at low Rayleigh number and infinite Prandtl number show that the convection can lock onto boundary temperature anomalies, but the corresponding effect in geodynamo simulations has either been absent or very intermittent. We have now succeeded in locking the magnetic field onto heat flux anomalies defined by the lower mantle seismic shear wave velocity by using low Rayleigh number, low inertia, and high (but not implausible) lateral variations in heat flux. The resulting surface field shows a remarkable resemblance to the present geomagnetic field, with 4 symmetric concentrations of magnetic flux. The position of these 4 lobes relative to the tangent cylinder give some clues to the degree of smoothing imposed by the inversion used to generate core field models. The observations appear to indicate that the correct regime for modelling the geodynamo is low Rayleigh number and low inertia, which demands an explanation.
DE: 1507 Core processes (1213, 8115)
DE: 1510 Dynamo: theories and simulations
DE: 1522 Paleomagnetic secular variation
DE: 1560 Time variations: secular and longer
DE: 7270 Tomography (6982, 8180)
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005