paper

Large Scale Azimuthal Structures Of Turbulence In Accretion Disks - Dynamo triggered variability of accretion

arXiv:1110.0961 · doi:10.1088/0004-637X/744/2/144

Abstract

We investigate the significance of large scale azimuthal, magnetic and velocity modes for the MRI turbulence in accretion disks. We perform 3D global ideal MHD simulations of global stratified proto-planetary disk models. Our domains span azimuthal angles of π/4, π/2, πand 2π. We observe up to 100% stronger magnetic fields and stronger turbulence for the restricted azimuthal domain models π/2 and π/4 compared to the full 2πmodel. We show that for those models, the Maxwell Stress is larger due to strong axisymmetric magnetic fields, generated by the αΩdynamo. Large radial extended axisymmetric toroidal fields trigger temporal magnification of accretion stress. All models display a positive dynamo-αin the northern hemisphere (upper disk). The parity is distinct in each model and changes on timescales of 40 local orbits. In model 2π, the toroidal field is mostly antisymmetric in respect to the midplane. The eddies of the MRI turbulence are highly anisotropic. The major wavelengths of the turbulent velocity and magnetic fields are between one and two disk scale heights. At the midplane, we find magnetic tilt angles around 8-9 degree increasing up to 12-13 degree in the corona. We conclude that an azimuthal extent of πis sufficient to reproduce most turbulent properties in 3D global stratified simulations of magnetised accretion disks.

accepted for publication in ApJ

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