Large- and Small-Scale Dynamo Action

Abstract

For an idealized model of helically forced flow in an extended domain, we have investigated the interaction between dynamo action on different spatial scales. The evolution of the magnetic field is studied numerically; from an initial state of weak magnetization, through the kinematic and into the dynamic regime. We show how the choice of initial conditions is a crucial factor in determining the structure of the magnetic field at subsequent times. Furthermore, with initial conditions chosen to favour the growth of the small-scale field, the evolution of the large-scale magnetic field can be described in terms of the α-effect of mean field magnetohydrodynamics.