Mean-field dynamos in random Arnold-Beltrami-Childress and Roberts flows

TL;DR

This paper investigates how time-fluctuating parameters in ABC and Roberts flows can enable large-scale magnetic field growth, overcoming limitations of stationary flows, through a mean-field dynamo approach.

Contribution

It derives new mean-field dynamo equations for fluctuating ABC and Roberts flows, showing nonstationarity can facilitate large-scale magnetic field growth.

Findings

Large-scale magnetic fields can grow with positive growth rates in fluctuating flows.

Nonstationarity removes the obstacle in large-scale dynamo action.

Growth rates are not limited by molecular magnetic diffusivity.

Abstract

We study magnetic field evolution in flows with fluctuating in time governing parameters in electrically conducting fluid. We use a standard mean-field approach to derive equations for large-scale magnetic field for the fluctuating ABC-flow as well as for the fluctuating Roberts flow. The derived mean-field dynamo equations have growing solutions with growth rate of the large-scale magnetic field which is not controlled by molecular magnetic diffusivity. Our study confirms the Zeldovich idea that the nonstationarity of the fluid flow may remove the obstacle in large-scale dynamo action of classic stationary flows.