Local Behavior of the Magnetorotational Instability in Accretion Disks

Abstract

The nonlinear evolutions of magnetorotational instability (MRI) in accretion disks are investigated using multi‐dimensional MHD simulations. We focus on the dependence of the saturation level of the MRI on physical quantities. The saturated Maxwell stress shows a weak power‐law dependence on the gas pressure in the nonlinear state. A predictor function of the saturation level is obtained and found to be inconsistent with the assumption of the standard alpha parameter. During the saturated turbulence, the exponential amplification of the magnetic field due to channel flow growth is roughly balanced with Sweet‐Parker type magnetic reconnection. In order to understand the saturation mechanism of the MRI, further simulations and theoretical analysis would be required.