Energy transfers during dynamo reversals -

Mishra, Pankaj and Gissinger, Christophe and Dormy, Emmanuel and Fauve, StephanEPL 104,

(2013) LPS

Abstract : Using direct numerical simulations of the equations of
magnetohydrodynamics, we study reversals of the magnetic field generated
by the flow of an electrically conducting fluid in a sphere. We show
that at low magnetic Prandtl numbers, Pm = 0.5, the decrease of magnetic
energy, ohmic dissipation and power of the Lorentz force during a
reversal is followed by an increase of the power injected by the force
driving the flow and an increase of viscous dissipation. Cross
correlations show that the power of the Lorentz force is in advance with
respect to the other energy flows. We also observe that during a
reversal, the maximum of the magnetic energy density migrates from one
hemisphere to the other and comes back to its initial position, in
agreement with recent experimental observations. For larger magnetic
Prandtl numbers (Pm - 1, 2), the magnetic field reversals do not display
these trends and strongly differ one from another. Copyright (C) EPLA,
2013