WKB thresholds of standard, helical, and azimuthal magnetorotational instability
Abstract
We consider rotating flows of an electrically conducting, viscous and resistive fluid in an external magnetic field with arbitrary combinations of axial and azimuthal components. Within the short-wavelength approximation, the local stability of the flow is studied with respect to perturbations of arbitrary azimuthal wavenumbers. In the limit of vanishing magnetic Prandtl number (Pm) we find that the maximum critical Rossby number (Ro) for the occurrence of the magnetorotational instability (MRI) is universally governed by the Liu limit {Ro}Liu=2-2√{2}≈ -0.828$ which is below the value for Keplerian rotation Ro Kepler = -0.75.
- Publication:
-
Feeding Compact Objects: Accretion on All Scales
- Pub Date:
- February 2013
- DOI:
- 10.1017/S1743921312019771
- Bibcode:
- 2013IAUS..290..233K
- Keywords:
-
- Magnetorotational instability;
- WKB approximation;
- accretion disks