Spectrum Of Global Magnetorotational Instability In A Narrow Transition Layer
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The global magnetorotational instability is investigated for a configuration in which the rotation frequency changes only in a narrow transition region. If the vertical wavelength of the unstable mode is of the same order or smaller than the width of this region, the growth rates can differ significantly from those given by a local analysis. In addition, the nonaxisymmetric spectrum admits overstable modes with a nontrivial dependence on azimuthal wavelength, a feature missed by the local theory. In the limit of vanishing transition region width, the Rayleigh-centrifugal instability is recovered in the axisymmetric case, and the Kelvin-Helmholtz instability in the nonaxisymmetric case.