Effects of alpha-effect fluctuations on simple nonlinear dynamo models

TL;DR

This paper explores how fluctuations in the alpha-effect influence magnetic field generation in nonlinear dynamo models, revealing mechanisms for dynamo action even with zero mean alpha and analyzing stability and solution properties.

Contribution

It extends previous models to include spatially varying alpha fluctuations, demonstrating their potential to drive dynamo action independently of the mean alpha value.

Findings

Fluctuations can enable magnetic field generation with zero mean alpha.

The stability and frequency of dynamo solutions depend on fluctuation characteristics.

The study links asymptotic theory with explicit simulations of fluctuating alpha models.

Abstract

We investigate the interaction of a fluctuating alpha-effect with large-scale shear in a simple nonlinear 1-dimensional dynamo wave model. We firstly extend the calculations of Proctor (2007, MNRAS, 41, L39-L42) to include spatial variation of the fluctuations, and find that there can be a mechanism for magnetic field generation, even when the mean alpha is zero, provided the spatiotemporal spectrum of the fluctuations has an appropriate form. We investigate mean-field dynamo action when the new term arising from the fluctuations is non-zero, and present results concerning the stability and frequency of the solutions and parity selection in the nonlinear regime. The relation between the asymptotic theory and explicit simulation of a traditional mean-field model with a fluctuating function for the alpha-effect term is discussed.