Mach Number Dependence of Turbulent Magnetic Field Amplification: Solenoidal versus Compressive Flows

TL;DR

This study investigates how Mach number influences turbulent magnetic field amplification in magnetohydrodynamical simulations, revealing differences in growth, saturation, and geometry between solenoidal and compressive flows across subsonic to supersonic regimes.

Contribution

It provides a comparative analysis of magnetic dynamo efficiency and characteristics in solenoidal versus compressive turbulence across a wide Mach number range.

Findings

Magnetic amplification decreases at the transition from subsonic to supersonic flows due to shocks.

Solenoidal forcing results in more efficient dynamo action than compressive forcing.

Magnetic field geometries and saturation levels vary significantly with Mach number and forcing type.

Abstract

We study the growth rate and saturation level of the turbulent dynamo in magnetohydrodynamical simulations of turbulence, driven with solenoidal (divergence-free) or compressive (curl-free) forcing. For models with Mach numbers ranging from 0.02 to 20, we find significantly different magnetic field geometries, amplification rates, and saturation levels, decreasing strongly at the transition from subsonic to supersonic flows, due to the development of shocks. Both extreme types of turbulent forcing drive the dynamo, but solenoidal forcing is more efficient, because it produces more vorticity.