A growing dynamo from a saturated Roberts flow dynamo

TL;DR

This paper demonstrates through simulations and theory that the quenched velocity field of a saturated nonlinear dynamo can itself generate a magnetic field, indicating a potential common property of nonlinear dynamos.

Contribution

It shows that the quenched velocity field in a saturated nonlinear dynamo can act as a kinematic dynamo, extending previous findings to more complex turbulent systems.

Findings

Quenched velocity fields can act as dynamos.

Supports the idea that this is common in nonlinear dynamos.

Provides a method to test nonlinear mean-field dynamo theories.

Abstract

Using direct simulations, weakly nonlinear theory and nonlinear mean-field theory, it is shown that the quenched velocity field of a saturated nonlinear dynamo can itself act as a kinematic dynamo. The flow is driven by a forcing function that would produce a Roberts flow in the absence of a magnetic field. This result confirms an analogous finding by F. Cattaneo & S. M. Tobias (arXiv:0809.1801) for the more complicated case of turbulent convection, suggesting that this may be a common property of nonlinear dynamos; see also the talk given also online at the Kavli Institute for Theoretical Physics (http://online.kitp.ucsb.edu/online/dynamo_c08/cattaneo). It is argued that this property can be used to test nonlinear mean-field dynamo theories.