HR: 09:21h
AN: MR41A-07 INVITED     [Abstracts]
TI: Numerical Models of the Geodynamo - Can They be Scaled to the Core?
AU: * Christensen, U R
EM: christensen@linmpi.mpg.de
AF: Max-Planck Institute for Solar System Research, Max-Planck Strasse 2 , Katlenburg-Lindau, 37191 Germany
AU: Aubert, J
EM: jaubert@gwdg.de
AF: Max-Planck Institute for Solar System Research, Max-Planck Strasse 2 , Katlenburg-Lindau, 37191 Germany
AB: Numerical dynamo models have been successful in the sense that they reproduce many properties of the geomagnetic field, such as its strength, dipole dominance, secular variation and stochastic reversals. They show that core-mantle coupling may explain non-axisymmetric features in the long-term magnetic field, for example preferred paths of the virtual geomagnetic pole during reversals. However, doubts remain on how realistic these models are, because several key parameters are far from Earth-like. Systematic parameter studies have become affordable and their goal is to establish scaling laws for the dependence of dynamo properties on the control parameters that can be extrapolated to Earth values. In a first step we recently derived a relation between the ohmic dissipation time and the magnetic Reynolds number. From this we estimate a rather moderate power requirement of the geodynamo, which implies that the inner core may be older than 2.5 Gyr. The amplitude of the zonal flow, which can be inferred from secular variation, scales with the square root of the buoyancy flux in the core. Assuming a dominant compositional source of buoyancy, this provides a maximum estimate of 0.1 mm/yr for the growth of the inner core, in agreement with an early formation of the inner core. An ambitious goal for the future is to determine what parameters control the strength of the magnetic field.
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 8130 Heat generation and transport
DE: 1507 Core processes (8115)
DE: 1510 Dynamo theories
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting