Efficient small-scale dynamo in solar convection zone

TL;DR

This study uses high-resolution MHD simulations to explore small-scale dynamo action in the solar convection zone, revealing significant magnetic feedback on convection and implications for solar dynamo modeling.

Contribution

It demonstrates the conditions under which small-scale dynamo action reaches near equipartition in the solar convection zone and analyzes its effects on convection and energy transport.

Findings

Magnetic field strength reaches 95% of equipartition at high resolution.

Lorentz force significantly reduces convection velocity.

Magnetic suppression of entropy mixing enhances convective efficiency.

Abstract

We investigate small-scale dynamo action in the solar convection zone through a series of high resolution MHD simulations in a local Cartesian domain with 1$R_\odot$ (solar radius) of horizontal extent and a radial extent from 0.715 to 0.96$R_\odot$. The dependence of the solution on resolution and diffusivity is studied. For a grid spacing of less than 350 km, the root mean square magnetic field strength near the base of the convection zone reaches 95% of the equipartition field strength (i.e. magnetic and kinetic energy are comparable). For these solutions the Lorentz force feedback on the convection velocity is found to be significant. The velocity near the base of the convection zone is reduced to 50% of the hydrodynamic one. In spite of a significant decrease of the convection velocity, the reduction in the enthalpy flux is relatively small, since the magnetic field also suppresses the horizontal mixing of the entropy between up- and downflow regions. This effect increases the amplitude of the entropy perturbation and makes convective energy transport more efficient. We discuss potential implications of these results for solar global convection and dynamo simulations.