Dynamo effects in magnetorotational turbulence with finite thermal diffusivity

Abstract

We investigate the saturation level of hydromagnetic turbulence driven by the magnetorotational instability in the case of vanishing net flux. Motivated by a recent paper of Bodo, Cattaneo, Mignone, & Rossi, we here focus on the case of a non-isothermal equation of state with constant thermal diffusivity. The central aim of the paper is to complement the previous result with closure parameters for mean-field dynamo models, and to test the hypothesis that the dynamo is affected by the mode of heat transport. We perform computer simulations of local shearing-box models of stratified accretion disks with approximate treatment of radiative heat transport, which is modeled via thermal conduction. We study the effect of varying the (constant) thermal diffusivity, and apply different vertical boundary conditions. In the case of impenetrable vertical boundaries, we confirm the transition from mainly conductive to mainly convective vertical heat transport below a critical thermal diffusivity. This transition is however much less dramatic when more natural outflow boundary conditions are applied. Similarly, the enhancement of magnetic activity in this case is less pronounced. Nevertheless, heating via turbulent dissipation determines the thermodynamic structure of accretion disks, and clearly affects the properties of the related dynamo. This effect may however have been overestimated in previous work, and a careful study of the role played by boundaries will be required.

7 pages, 9 figures, accepted for publication in ApJ

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• Local simulations of MRI turbulence with meshless methods
• Convective Quenching of Field Reversals in Accretion Disc Dynamos
• Zero net flux MRI-turbulence in disks $-$ sustenance scheme and magnetic Prandtl number dependence
• Fully Convective Magnetorotational Turbulence in Stratified Shearing Boxes
• Finite-time response of dynamo mean-field effects in magnetorotational turbulence
• MRI turbulence in vertically stratified accretion discs at large magnetic Prandtl numbers
• Quantifying the effect of turbulent magnetic diffusion on the growth rate of the magneto-rotational instability
• Magnetohydrodynamic convection in accretion discs
• Stability Analysis of Convection in the Intracluster Medium
• Magnetic Helicities and Dynamo Action in Magneto-rotationally Driven Turbulence
• Study of MRI in stratified viscous plasma configuration