Local Accretion Disk Dynamo Models from Azimuthally Averaged 3D Simulations

Magnetized turbulent systems such as accretion disks can be numerically evolved for long times much more cheaply if axisymmetry is assumed. However, the field in such 2D simulations unphysically decays unless dynamo terms, representing the underlying nonaxisymmetry, are explicitly added to the induction equation. Thus far, such simulations have commonly assumed simple, isotropic forms of the dynamo coefficient tensors. While this does yield magnetic fields that do not die off, it is unclear that it is necessarily correct. We test this assumption by azimuthally averaging data from a 3D black hole accretion simulation carried out by the IllinoisGRMHD code. Multiple local models, in which the dynamo electromotive force is a linear function of the local azimuthally averaged magnetic field and current, are tested, but no statistically reliable model could be attained. However, we do find that most of the turbulent kinetic and magnetic energy in the disk is not in the azimuthal mean, but in the RMS deviation, although the jet is mostly axisymmetric. As such, we conclude by discussing more general models that incorporate turbulent energy, dynamo electromotive force and momentum transport.