A novel type of intermittency in a nonlinear dynamo in a compressible flow

TL;DR

This paper investigates a new type of intermittency in nonlinear dynamo systems within compressible flows, revealing how magnetic fields transition between coherent and incoherent states, with implications for stellar magnetic variability.

Contribution

It introduces a novel intermittency phenomenon in mean-field dynamos, observed through numerical simulations of compressible MHD turbulence at low Prandtl numbers.

Findings

Discovered a new intermittency type with magnetic field switching between coherent and incoherent states.

Identified the evolution of the dynamo system through different intermittency regimes.

Discussed relevance to stellar magnetic field variability.

Abstract

The transition to intermittent mean--field dynamos is studied using numerical simulations of isotropic magnetohydrodynamic turbulence driven by a helical flow. The low-Prandtl number regime is investigated by keeping the kinematic viscosity fixed while the magnetic diffusivity is varied. Just below the critical parameter value for the onset of dynamo action, a transient mean--field with low magnetic energy is observed. After the transition to a sustained dynamo, the system is shown to evolve through different types of intermittency until a large--scale coherent field with small--scale turbulent fluctuations is formed. Prior to this coherent field stage, a new type of intermittency is detected, where the magnetic field randomly alternates between phases of coherent and incoherent large--scale spatial structures. The relevance of these findings to the understanding of the physics of mean--field dynamo and the physical mechanisms behind intermittent behavior observed in stellar magnetic field variability are discussed.