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

TL;DR

This study uses 3D global MHD simulations to explore how azimuthal domain size affects turbulence and magnetic field structures in accretion disks, revealing that a zimuthal extent captures most turbulent features.

Contribution

It demonstrates that a zimuthal domain in simulations is sufficient to replicate key turbulence characteristics in accretion disks, highlighting the role of large-scale magnetic structures.

Findings

Azimuthal extent of h captures most turbulence properties.

Large azimuthal domains produce stronger magnetic fields and turbulence.

Dynamo processes generate axisymmetric magnetic fields influencing accretion stress.

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 \pi/4, \pi/2, \pi and 2\pi. We observe up to 100% stronger magnetic fields and stronger turbulence for the restricted azimuthal domain models \pi/2 and \pi/4 compared to the full 2\pi model. We show that for those models, the Maxwell Stress is larger due to strong axisymmetric magnetic fields, generated by the \alpha \Omega dynamo. Large radial extended axisymmetric toroidal fields trigger temporal magnification of accretion stress. All models display a positive dynamo-\alpha in the northern hemisphere (upper disk). The parity is distinct in each model and changes on timescales of 40 local orbits. In model 2\pi, 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 \pi is sufficient to reproduce most turbulent properties in 3D global stratified simulations of magnetised accretion disks.