Modeling Magnetorotational Turbulence in Protoplanetary Disks with Dead Zones

TL;DR

This paper uses 3D MHD simulations to empirically model how magnetorotational turbulence in protoplanetary disks is influenced by dead zones, magnetic flux, and resistivity, providing predictive relations for disk turbulence structure.

Contribution

It introduces empirical formulas linking turbulence characteristics to magnetic flux and resistivity profiles in stratified protoplanetary disks.

Findings

Vertical magnetic flux characterizes turbulence structure.

Turbulent quantities scale with accretion stresses.

Empirical formulas predict turbulence based on magnetic flux and resistivity.

Abstract

Turbulence driven by magnetorotational instability (MRI) crucially affects the evolution of solid bodies in protoplanetary disks. On the other hand, small dust particles stabilize MRI by capturing ionized gas particles needed for the coupling of the gas and magnetic fields. To provide an empirical basis for modeling the coevolution of dust and MRI, we perform three-dimensional, ohmic-resistive MHD simulations of a vertically stratified shearing box with an MRI-inactive "dead zone" of various sizes and with a net vertical magnetic flux of various strengths. We find that the vertical structure of turbulence is well characterized by the vertical magnetic flux and three critical heights derived from the linear analysis of MRI in a stratified disk. In particular, the turbulent structure depends on the resistivity profile only through the critical heights and is insensitive to the details of the resistivity profile. We discover scaling relations between the amplitudes of various turbulent quantities (velocity dispersion, density fluctuation, vertical diffusion coefficient, and outflow mass flux) and vertically integrated accretion stresses. We also obtain empirical formulae for the integrated accretion stresses as a function of the vertical magnetic flux and the critical heights. These empirical relations allow to predict the vertical turbulent structure of a protoplanetary disk for a given strength of the magnetic flux and a given resistivity profile.