Morphology of field reversals in turbulent dynamos
Laboratoire de Physique Statistique, Ecole Normale Supérieure, UPMC Université Paris 6, Université Paris Diderot, CNRS - 24 rue Lhomond, 75005 Paris, France, EU
2 MAG (IPGP/ENS), CNRS UMR 7154, LRA, Ecole Normale Supérieure - 24 Rue Lhomond, 75231 Paris Cedex 05, France, EU
Accepted: 20 May 2010
We show that the modes involved in the dynamics of reversals of the magnetic field generated by the flow of an electrically conducting fluid in a spherical domain, strongly depend on the magnetic Prandtl number Pm, i.e., the ratio between viscous and magnetic diffusivities. For Pm ~ 1, the axial dipolar field reverses in the presence of a strong equatorial dipolar component, whereas for Pm < 0.5, field reversals mostly involve axisymmetric modes, axial magnetic dipole and quadrupole coupled through a broken symmetry of the flow. Using symmetry arguments, we write a dynamical system for these three modes that qualitatively reproduces the main features of the reversals observed in direct simulations for small Pm.
PACS: 91.25.Cw – Origins and models of the magnetic field; dynamo theories / 47.65.-d – Magnetohydrodynamics and electrohydrodynamics
© EPLA, 2010