LES of turbulent convection in solar-type stars and formation of large-scale magnetic structures

TL;DR

This paper uses advanced LES techniques with a new subgrid-scale model to study how turbulent convection in solar-type stars leads to large-scale magnetic structures, revealing threshold conditions for magnetic flux tube formation.

Contribution

Introduces a novel subgrid-scale turbulence model (TELF-Model) for MHD LES, enabling detailed simulation of magnetic flux tube formation in stellar convection zones.

Findings

Magnetic flux tubes form when initial magnetic field exceeds ~100 G.

Vertical profiles of turbulence and magnetic fluctuations characterized.

Threshold magnetic field strength for flux tube formation confirmed.

Abstract

In this study we investigate the effects of turbulent convection on formation of large-scale inhomogeneous magnetic structures by means of Large-Eddy Simulation (LES) for convection in solar-type stars. The main idea of this study is the implementation of a new subgrid-scale model for the effective Lorentz force in a three-dimensional nonlinear radiative magnetohydrodynamics (MHD) code developed for simulating the upper solar convection zone and lower atmosphere. To this end we derived the energy budget equations, which include the effects of the subgrid-scale turbulence on the Lorentz-force, and implemented the new subgrid-scale turbulence model (TELF-Model) in a three-dimensional nonlinear MHD LES code. Using imposed initial vertical and horizontal uniform magnetic fields in LES with the TELF-Model, we have shown that the magnetic flux tubes formation is started when the initial mean magnetic field is larger than a threshold value (about 100 G). This is in agreement with the theoretical studies by Rogachevskii and Kleeorin (2007). We have determined the vertical profiles of the velocity and magnetic fluctuations, total MHD energy and anisotropy of turbulent magneto-convection, kinetic and current and cross helicities.