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Dynamo generated by the centrifugal instability

Florence Marcotte1,2,* and Christophe Gissinger3

  • 1Laboratoire de RadioAstronomie, Ecole Normale Superieure, CNRS, 24 rue Lhomond, 75005 Paris, France
  • 2Institut de Physique du Globe de Paris, CNRS, 1 rue Jussieu, 75005 Paris, France
  • 3Laboratoire de Physique Statistique, Ecole Normale Superieure, CNRS, 24 rue Lhomond, 75005 Paris, France

  • *Corresponding author: marcotte@lra.ens.fr
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Phys. Rev. Fluids 1, 063602 – Published 5 October, 2016

DOI: https://doi.org/10.1103/PhysRevFluids.1.063602

Abstract

We present a scenario for magnetic field amplification where an electrically conducting fluid is confined in a differentially rotating, spherical shell with thin aspect ratio. When the angular momentum sufficiently decreases outwards, a hydrodynamic instability develops in the equatorial region, characterized by pairs of counter-rotating toroidal vortices similar to those observed in cylindrical Couette flow. These spherical Taylor-Couette vortices generate a subcritical dynamo magnetic field dominated by nonaxisymmetric components. We show that the critical magnetic Reynolds number seems to reach a constant value at large Reynolds number and that the global rotation can strongly decrease the dynamo onset. Our numerical results are understood within the framework of a simple dynamical system, and we propose a low-dimensional model for subcritical dynamo bifurcations. Implications for both laboratory dynamos and astrophysical magnetic fields are finally discussed.

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Phys. Rev. Fluids 1, 063602– Published 5 October, 2016
  • Received 11 June 2016

©2016 American Physical Society

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