Small-scale dynamos in simulations of stratified turbulent convection

TL;DR

This study uses high-resolution simulations to explore the conditions under which small-scale dynamos operate in stratified turbulent convection, revealing that dynamo excitation depends on magnetic Reynolds number and Prandtl number.

Contribution

It provides new insights into the excitation and saturation of small-scale dynamos at low magnetic Prandtl numbers through detailed numerical simulations.

Findings

Critical magnetic Reynolds number increases as Prandtl number decreases.

Dynamo growth rate scales with the square root of Rm.

No logarithmic growth of the dynamo growth rate observed.

Abstract

Small-scale dynamo action is often held responsible for the generation of quiet-Sun magnetic fields. We aim to determine the excitation conditions and saturation level of small-scale dynamos in non-rotating turbulent convection at low magnetic Prandtl numbers. We use high resolution direct numerical simulations of weakly stratified turbulent convection. We find that the critical magnetic Reynolds number for dynamo excitation increases as the magnetic Prandtl number is decreased, which might suggest that small-scale dynamo action is not automatically evident in bodies with small magnetic Prandtl numbers as the Sun. As a function of the magnetic Reynolds number (${\rm Rm}$), the growth rate of the dynamo is consistent with an ${\rm Rm}^{1/2}$ scaling. No evidence for a logarithmic increase of the growth rate with ${\rm Rm}$ is found.