Bipolar magnetic structures driven by stratified turbulence with a coronal envelope
Abstract
We report the spontaneous formation of bipolar magnetic structures in direct numerical simulations of stratified forced turbulence with an outer coronal envelope. The turbulence is forced with transverse random waves only in the lower (turbulent) part of the domain. Our initial magnetic field is either uniform in the entire domain or confined to the turbulent layer. After about 1--2 turbulent diffusion times, a bipolar magnetic region of vertical field develops with two coherent circular structures that live during one turbulent diffusion time, and then decay during 0.5 turbulent diffusion times. The resulting magnetic field strengths inside the bipolar region are comparable to the equipartition value with respect to the turbulent kinetic energy. The bipolar magnetic region forms a loop-like structure in the upper coronal layer. We associate the magnetic structure formation with the negative effective magnetic pressure instability in the two-layer model.
Cite
@article{arxiv.1308.1080,
title = {Bipolar magnetic structures driven by stratified turbulence with a coronal envelope},
author = {Jörn Warnecke and Illa R. Losada and Axel Brandenburg and Nathan Kleeorin and Igor Rogachevskii},
journal= {arXiv preprint arXiv:1308.1080},
year = {2013}
}
Comments
7 pages, 5 figures, published in ApJL