Speaker
A. Brandenburg
Description
We present the first demonstration of the negative effective
magnetic pressure instability in direct numerical
simulations of stably stratified, externally forced,
isothermal hydromagnetic turbulence in the regime of large
plasma beta. By the action of this instability, an initially
uniform horizontal magnetic field forms flux concentrations
whose scale is large compared to the turbulent scale. We
further show that the magnetic energy of these large-scale
structures is only weakly dependent on the magnetic Reynolds
number, provided its value is large enough for the
instability to be excited. Our results support earlier
mean-field calculations and analytic work which identified
this instability. Applications to the formation of active
regions in the Sun are discussed.
[Astrophys. J. Lett. 740, L50 (2011) ]
