Tuesday, August 6, 2013

1308.1080 (Jörn Warnecke et al.)

Bipolar magnetic structures driven by stratified turbulence with a coronal envelope    [PDF]

Jörn Warnecke, Illa R. Losada, Axel Brandenburg, Nathan Kleeorin, Igor Rogachevskii
We report the spontaneous formation of a bipolar magnetic structure in a direct numerical simulation of stratified forced turbulence with an outer coronal envelope. We impose a weak horizontal magnetic field in the entire domain. The turbulence is forced with transverse random waves in the lower (turbulent) part of the domain. After about 1.5 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 are comparable to the equipartition value with respect to the turbulent kinetic energy. The bipolar magnetic region forms a loop-like structure in the corona. We associate the magnetic structure formation with the negative effective magnetic pressure instability in the two-layer model.
View original: http://arxiv.org/abs/1308.1080

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