http://arxiv.org/abs/1803.08557
Magnetohydrodynamic instabilities play an important role in accretion disks systems. Besides the well-known effects of the magnetorotational instability (MRI), the Parker-Rayleigh-Taylor instability (PRTI) also arises as an important mechanism to help in the formation of the coronal region around an accretion disk and in the production of magnetic reconnection events similar to those occurring in the solar corona. In this work, we have performed three-dimensional magnetohydrodynamical (3D-MHD) shearing-box numerical simulations of accretion disks with an initial stratified density distribution and a strong azimuthal magnetic field with a ratio between the thermal and magnetic pressures of the order of unity. This study aimed at verifying the role of these instabilities on the formation of the coronal region and especially on the driving of turbulence and magnetic reconnection. Our simulations revealed an initial formation of large-scale magnetic loops due to the PRTI followed by the development of a nearly steady-state turbulence driven by both instabilities. We have employed an algorithm to identify the presence of current sheets produced by the encounter of magnetic flux ropes of opposite polarity in the turbulent regions of both the corona and the disk. We computed the magnetic reconnection rates in these locations obtaining average reconnection velocities in Alfv\’en speed units of the order of $0.13 \pm 0.9$ in the accretion disk and $0.17 \pm 0.10 $ in the coronal region (with mean peak values of order of $0.2$), which are consistent with the predictions of the theory of turbulence-induced fast reconnection.
L. Kadowaki, E. Pino and J. Stone
Mon, 26 Mar 18
31/43
Comments: 23 pages, 15 figures, submitted to ApJ
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