Time scales separation for dynamo action
Classical Physics
2009-11-13 v2 Astrophysics
Fluid Dynamics
Abstract
The study of dynamo action in astrophysical objects classically involves two timescales: the slow diffusive one and the fast advective one. We investigate the possibility of field amplification on an intermediate timescale associated with time dependent modulations of the flow. We consider a simple steady configuration for which dynamo action is not realised. We study the effect of time dependent perturbations of the flow. We show that some vanishing low frequency perturbations can yield exponential growth of the magnetic field on the typical time scale of oscillation. The dynamo mechanism relies here on a parametric instability associated with transient amplification by shear flows. Consequences on natural dynamos are discussed.
Cite
@article{arxiv.0804.0115,
title = {Time scales separation for dynamo action},
author = {Emmanuel Dormy and David Gerard-Varet},
journal= {arXiv preprint arXiv:0804.0115},
year = {2009}
}