Wave-driven dynamo action in spherical MHD systems

Abstract

Hydrodynamic and magnetohydrodynamic numerical studies of a mechanically forced two-vortex flow inside a sphere are reported. The simulations are performed in the intermediate regime between the laminar flow and developed turbulence where a hydrodynamic instability is found to generate internal waves with a characteristic m=2 zonal wave number. It is shown that this time-periodic flow acts as a dynamo although snapshots of the flow as well as the mean flow are not dynamos. The magnetic fields' growth rate exhibits resonance effects depending on the wave frequency. Furthermore, a cyclic self-killing and self-recovering dynamo based on the relative alignment of the velocity and magnetic fields is presented. The phenomena are explained in terms of a mixing of non-orthogonal eigenstates of the time dependent linear operator of the magnetic induction equation. The potential relevance of this mechanism to dynamo experiments is discussed.

11 pages, 13 figures

References in corpus (5)

• Generation of magnetic field by dynamo action in a turbulent flow of liquid sodium
• Magnetohydrodynamic experiments on cosmic magnetic fields
• Numerical simulations of current generation and dynamo excitation in a mechanically-forced, turbulent flow
• Intermittent magnetic field excitation by a turbulent flow of liquid sodium
• Bypassing Cowling's theorem in axisymmetric fluid dynamos

Cited by in corpus (8)

• Impact of time-dependent non-axisymmetric velocity perturbations on dynamo action of von-Kármán-like flows
• A dynamo driven by zonal jets at the upper surface: Applications to giant planets
• Simulations of the kinematic dynamo onset of spherical Couette flows with smooth and rough boundaries
• Numerical simulation of laminar plasma dynamos in a cylindrical von Kármán flow
• Parametric instability in periodically perturbed dynamos
• Identification of vortexes obstructing the dynamo mechanism in laboratory experiments
• Laboratory experiments and numerical simulations on magnetic instabilities
• Scaling laws and bounds for the turbulent G.O. Roberts dynamo