Resolution Dependence of Magnetorotational Turbulence in the Isothermal Stratified Shearing Box

Ryan, Benjamin R.; Gammie, Charles F.; Fromang, Sebastien; Kestener, Pierre

Magnetohydrodynamic turbulence driven by the magnetorotational instability can provide diffusive transport of angular momentum in astrophysical disks, and a widely studied computational model for this process is the ideal, stratified, isothermal shearing box. Here we report results of a convergence study of such boxes up to a resolution of N = 256 zones per scale height, performed on blue waters at NCSA with ramses-gpu. We find that the time and vertically integrated dimensionless shear stress \overline{α }˜ {N}^{-1/3}, i.e., the shear stress is resolution dependent. We also find that the magnetic field correlation length decreases with resolution, λ ˜ {N}^{-1/2}. This variation is strongest at the disk midplane. We show that our measurements of \overline{α } are consistent with earlier studies, and we discuss possible reasons for the lack of convergence.