Chaotic behavior of Eulerian MHD turbulence

TL;DR

This paper investigates the chaotic dynamics of magnetohydrodynamic turbulence using numerical simulations, extending existing theories, and analyzing how magnetic helicity and dissipation influence predictability in such systems.

Contribution

It extends Ruelle theory to MHD turbulence, examines the effects of magnetic helicity on chaos, and links chaos growth to dissipation rates, providing new insights into turbulence predictability.

Findings

Lyapunov exponent varies with Reynolds and magnetic Prandtl numbers

Magnetic helicity reduces chaos, approaching elimination at maximum helicity

Linear growth of divergence between fields depends on dissipation rate

Abstract

We study the chaotic properties of a turbulent conducting fluid using direct numerical simulation in the Eulerian frame. The maximal Lyapunov exponent is measured for simulations with varying Reynolds number and magnetic Prandtl number. We extend the Ruelle theory of hydrodynamic turbulence to magnetohydrodynamic turbulence as a working hypothesis and find broad agreement with results. In other simulations we introduce magnetic helicity and these simulations show a diminution of chaos, which is expected to be eliminated at maximum helicity. We also find that the difference between two initially close fields grows linearly at late times, which was also recently found in hydrodynamics. This linear growth rate is found to be dependent on the dissipation rate of the relevant field. We discuss the important consequences this linear growth has on predictability. We infer that the chaos in the system is totally dominated by the velocity field and connect this work to real magnetic systems such as solar weather and confined plasmas.