Morphology of field reversals in turbulent dynamos

Author: Gissinger C.   Dormy E.   Fauve S.  

Publisher: Edp Sciences

E-ISSN: 1286-4854|90|4|49001-49001

ISSN: 0295-5075

Source: EPL (EUROPHYSICS LETTERS), Vol.90, Iss.4, 2010-06, pp. : 49001-49001

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Abstract

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.