[GTP] GTP-HAO Seminar at NCAR -March 27

[Silvia Gentile]

Joint GTP- HAO Seminar

Negative Effective Magnetic Pressure Instability: A possible mechanism 
for formation of active regions.
Dhrubaditya Mitra, NORDITA
Abstract:
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.
Refs:  ``Detection of negative effective magnetic pressure instability 
in turbulence simulations,'' Astrophys. J. Lett. 740, L50

March 27, 2012
Time: 1:30pm
Center Green Laboratory 1, South Auditorium




Silvia Gentile
NCAR IMAGe