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Geophys. J. Int. (2006) doi: 10.1111/j.1365-246X.2006.03009.x GJIGeomagnetism,rockmagnetismandpalaeomagnetism

Summary: Geophys. J. Int. (2006) doi: 10.1111/j.1365-246X.2006.03009.x
Scaling properties of convection-driven dynamos in rotating spherical
shells and application to planetary magnetic fields
U. R. Christensen1
and J. Aubert2
1Max-Planck-Institut fur Sonnensystemforschung, Katlenburg-Lindau, Germany. E-mail: christensen@mps.mpg.de
2Institut de Physique du Globe de Paris, Paris, France
Accepted 2006 March 17. Received 2006 March 17; in original form 2005 September 28
We study numerically an extensive set of dynamo models in rotating spherical shells, varying all
relevant control parameters by at least two orders of magnitude. Convection is driven by a fixed
temperature contrast between rigid boundaries. There are two distinct classes of solutions with
strong and weak dipole contributions to the magnetic field, respectively. Non-dipolar dynamos
are found when inertia plays a significant role in the force balance. In the dipolar regime the
critical magnetic Reynolds number for self-sustained dynamos is of order 50, independent of
the magnetic Prandtl number Pm. However, dynamos at low Pm exist only at sufficiently low
Ekman number E. For dynamos in the dipolar regime we attempt to establish scaling laws that fit
our numerical results. Assuming that diffusive effects do not play a primary role, we introduce
non-dimensional parameters that are independent of any diffusivity. These are a modified


Source: Aubert, Julien - Institut de Physique du Globe de Paris


Collections: Geosciences