title: Global Simulations of Differentially Rotating Magnetized Disks: Formation of Low-beta Filaments and Structured Coronae.
abstract: We present the results of three-dimensional global magnetohydrodynamic simulations of the Parker-shearing instability in a differentially rotating torus initially threaded by toroidal magnetic fields. An equilibrium model of a magnetized torus is adopted as an initial condition. When beta0=Pgas&solm0;Pmag approximately 1 at the initial state, magnetic flux buoyantly escapes from the disk and creates looplike structures similar to those in the solar corona. Inside the torus, the growth of nonaxisymmetric magnetorotational (or Balbus & Hawley) instability generates magnetic turbulence. Magnetic field lines are tangled on a small scale, but on a large scale they show low azimuthal wavenumber spiral structure. After several rotation periods, the system oscillates around a state with beta approximately 5. We found that magnetic pressure-dominated (beta<1) filaments are created in the torus. The volume filling factor of the region in which beta</=0.3 is 2%-10%. Magnetic energy release in such low-beta regions may lead to violent flaring activities in accretion disks and in galactic gas disks.
authors.initials: M
authors.lastname: Machida
authors.initials: MR
authors.lastname: Hayashi
authors.initials: R
authors.lastname: Matsumoto