Shearing box simulations of accretion disk winds

TL;DR

This paper uses shearing box simulations to study magnetically driven outflows from accretion disks, revealing different instability regimes and their potential impact on jet variability.

Contribution

It demonstrates the development of mass-flux instabilities in MRI-stable regimes and explores their characteristics using 2D shearing box models with improved boundary conditions.

Findings

Mass-flux instability occurs in high magnetic field regimes.

Low field strength instabilities develop rapidly and saturate at modest amplitudes.

High field strength leads to large-scale, long-wavelength instump.

Abstract

The launching process of a magnetically driven outflow from an accretion disk is investigated in a local, shearing box model which allows a study of the feedback between accretion and angular momentum loss. The mass-flux instability found in previous linear analyses of this problem is recovered in a series of 2D (axisymmetric) simulations in the MRI-stable (high magnetic field strength) regime. At low field strengths that are still sufficient to suppress MRI, the instability develops on a short radial length scale and saturates at a modest amplitude. At high field strengths, a long-wavelength "clump" instability of large amplitude is observed, with growth times of a few orbits. As speculated before, the unstable connection between disk and outflow may be relevant for the time dependence observed in jet-producing disks. The success of the simulations is due in a large part to the implementation of an effective wave-transmitting upper boundary condition.