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Negative Effective Magnetic Pressure Instability: A possible mechanism for formation of active regions

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  

Tuesday, March 27, 2012
Center Green Laboratory 1, South Auditorium

Lecture at 1:30pm

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Tuesday, March 27, 2012
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Tuesday, March 27, 2012