On the Nature of Magnetic Turbulence in Rotating, Shearing Flows

الأصل · EN

The local properties of turbulence driven by the magnetorotational instability (MRI) in rotating, shearing flows are studied in the framework of a shearing-box model. Based on numerical simulations, we propose that the MRI-driven turbulence comprises two components: the large-scale shear-aligned strong magnetic field and the small-scale fluctuations resembling magnetohydrodynamic (MHD) turbulence. The energy spectrum of the large-scale component is close to k⁻², whereas the spectrum of the small-scale component agrees with the spectrum of strong MHD turbulence k⁻³/². While the spectrum of the fluctuations is universal, the outer-scale characteristics of the turbulence are not; they depend on the parameters of the system, such as the net magnetic flux. However, there is remarkable universality among the allowed turbulent states -- their intensity v₀ and their outer scale λ₀ satisfy the balance condition v₀/λ₀ dΩ/d r, where dΩ/d r is the local orbital shearing rate of the flow. Finally, we find no sustained dynamo action in the Pm=1 zero net-flux case for Reynolds numbers as high as 45000, casting doubts on the existence of an MRI dynamo in the Pm≤ 1 regime.