Turbulent small-scale dynamo action in solar surface simulations

TL;DR

This paper demonstrates that solar surface simulations exhibit a small-scale turbulent dynamo driven primarily by fluid motion stretching magnetic field lines, with energy transfer analyzed through derived equations.

Contribution

It provides a detailed derivation of energy transfer functions in compressible MHD and identifies the dominant dynamo mechanism as stretching by inertial-range motions.

Findings

Small-scale magnetic energy is mainly generated by stretching of magnetic field lines.

The dynamo mechanism is identified as a small-scale turbulent dynamo.

Scales involved decrease with increasing Reynolds number.

Abstract

We demonstrate that a magneto-convection simulation incorporating essential physical processes governing solar surface convection exhibits turbulent small-scale dynamo action. By presenting a derivation of the energy balance equation and transfer functions for compressible magnetohydrodynamics (MHD), we quantify the source of magnetic energy on a scale-by-scale basis. We rule out the two alternative mechanisms for the generation of small-scale magnetic field in the simulations: the tangling of magnetic field lines associated with the turbulent cascade and Alfvenization of small-scale velocity fluctuations ("turbulent induction"). Instead, we find the dominant source of small-scale magnetic energy is stretching by inertial-range fluid motions of small-scale magnetic field lines against the magnetic tension force to produce (against Ohmic dissipation) more small-scale magnetic field. The scales involved become smaller with increasing Reynolds number, which identifies the dynamo as a small-scale turbulent dynamo.