An Incoherent α-Ω Dynamo in Accretion Disks

We use the mean-field dynamo equations to show that spatially and temporally incoherent fluctuations in the helicity in mirror-symmetric turbulence in a shearing flow can generate a large-scale, coherent magnetic field. We illustrate this effect with simulations of a few simple systems. For statistically homogeneous turbulence, we find that the dynamo growth rate is roughly τeddy−1/3τshear−2/3Neddy−1/3(λeddy/LB)2/3, where τeddy is the eddy …