Astronomy and Astrophysics – Astrophysics
Scientific paper
2002-05-22
Astrophys.J. 577 (2002) 534
Astronomy and Astrophysics
Astrophysics
43 pages, 8 tables, 20 figures, accepted for publication in ApJ, postscript version also available from http://www.astro.umd
Scientific paper
10.1086/342172
The nonlinear evolution of the magnetorotational instability (MRI) in weakly ionized accretion disks, including the effect of the Hall term and ohmic dissipation, is investigated using local three-dimensional MHD simulations and various initial magnetic field geometries. When the magnetic Reynolds number, Re_M \equiv v_A^2 / \eta \Omega (where v_A is the Alfven speed, \eta the magnetic diffusivity, and \Omega the angular frequency), is initially larger than a critical value Re_{M, crit}, the MRI evolves into MHD turbulence in which angular momentum is transported efficiently by the Maxwell stress. If Re_M < Re_{M, crit}, however, ohmic dissipation suppresses the MRI, and the stress is reduced by several orders of magnitude. The critical value is in the range of 1 - 30 depending on the initial field configuration. The Hall effect does not modify the critical magnetic Reynolds number by much, but enhances the saturation level of the Maxwell stress by a factor of a few. We show that the saturation level of the MRI is characterized by v_{Az}^2 / \eta \Omega, where v_{Az} is the Alfven speed in the nonlinear regime along the vertical component of the field. The condition for turbulence and significant transport is given by v_{Az}^2 / \eta \Omega \gtrsim 1, and this critical value is independent of the strength and geometry of the magnetic field or the size of the Hall term. If the magnetic field strength in an accretion disk can be estimated observationally, and the magnetic Reynolds number v_A^2 / \eta \Omega is larger than about 30, this would imply the MRI is operating in the disk.
Sano Takayoshi
Stone James M.
No associations
LandOfFree
The Effect of the Hall Term on the Nonlinear Evolution of the Magnetorotational Instability: II. Saturation Level and Critical Magnetic Reynolds Number does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Effect of the Hall Term on the Nonlinear Evolution of the Magnetorotational Instability: II. Saturation Level and Critical Magnetic Reynolds Number, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Effect of the Hall Term on the Nonlinear Evolution of the Magnetorotational Instability: II. Saturation Level and Critical Magnetic Reynolds Number will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-453969