On vertical variations of gas flow in protoplanetary disks and their impact on the transport of solids

Abstract

A major uncertainty in accretion disk theory is the nature and properties of gas turbulence, which drives transport in protoplanetary disks. The commonly used viscous prescription for the Maxwell-Reynolds stress tensor gives rise to a meridional circulation where flow is outward near the midplane and inward away from it. This meridional circulation has been proposed as an explanation for the presence of high-temperature minerals (believed to be of inner solar system provenance) in comets. However, it has not been observed in simulations of magnetohydrodynamical (MHD) turbulence so far. In this study, we evaluate the extent to which the net transport of solids can be diagnostic of the existence of meridional circulation. To that end, we propose and motivate a prescription for MHD turbulence which has the same free parameters as the viscous one. We compare the effects of both prescriptions on the radial transport of small solid particles and find that their net, vertically integrated radial flux is actually quite insensitive to the flow structure for a given vertical average of the turbulence parameter $\alpha$, which we explain. Given current uncertainties on disk turbulence, one-dimensional models are thus most appropriate to investigate radial transport of solids. A corollary is that the presence of high-temperature material in comets cannot be considered an unequivocal diagnostic of meridional circulation. In fact, we argue that outward transport in viscous disk models is more properly attributed to turbulent diffusion rather than to the mean flows of the gas.

8 pages, 4 figures, accepted to Astronomy and Astrophysics

References in corpus (6)

• Global MHD simulations of stratified and turbulent protoplanetary discs. I. Model properties
• Local outflows from turbulent accretion disks
• Global MHD simulations of stratified and turbulent protoplanetary discs. II. Dust settling
• Two-Dimensional Transport of Solids in Viscous Protoplanetary Disks
• The magnetorotational instability as a jet launching mechanism
• Turbulent diffusion in protoplanetary discs: the effect of an imposed magnetic field

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• Vertical shear instability in two-moment radiation-hydrodynamical simulations of irradiated protoplanetary disks I. Angular momentum transport and turbulent heating
• Radial Transport and Meridional Circulation in Accretion Disks
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