Small-scale magnetohydrodynamic dynamos: from deterministic chaos to turbulence

TL;DR

This paper investigates how small-scale MHD dynamos transition from deterministic chaos to turbulence, using numerical simulations and observations, and introduces a framework based on distributed chaos and invariants to quantify this process.

Contribution

It presents a novel approach linking invariants and distributed chaos to describe the chaos-to-turbulence transition in small-scale MHD dynamos, supported by simulations and observations.

Findings

Randomization process characterizes the transition to turbulence.

Magnetohydrodynamic invariants control the degree of chaos.

Numerical results agree with geophysical and solar data.

Abstract

It is shown, using results of numerical simulations, and geophysical and solar observations, that the transition from deterministic chaos to hard turbulence in the magnetic field generated by the small-scale MHD dynamos occurs through a randomization process. This randomization process has been described using the notion of distributed chaos and the main parameter of distributed chaos has been used for quantifying the degree of randomization. The dissipative (Loitsianskii and Birkhoff-Saffman integrals) and ideal (magnetic helicity) magnetohydrodynamic invariants control the randomization process and determine the degree of randomization in different MHD flows, directly or through the Kolmogorov-Iroshnikov phenomenology (the magneto-inertial range of scales as a precursor of hard turbulence). Despite the considerable differences in the scales and physical parameters, the results of numerical simulations are in quantitative agreement with the geophysical and solar observations in the frames of this approach. The Hall magnetohydrodynamic dynamo has been also briefly discussed in this context.