RADIALLY EXTENDED, STRATIFIED, LOCAL MODELS OF ISOTHERMAL DISKS

We consider local, stratified, numerical models of isothermal accretion disks. The novel feature of our treatment is that radial extent L-x and azimuthal extent L-y satisfy H << L-x, L-y << R, where H is the scale height and R is the local radius. This enables us to probe mesoscale structure in stratified thin disks. We evolve the model at several resolutions, sizes, and initial magnetic field strengths. Consistent with earlier work, we find that the saturated, turbulent state consists of a weakly magnetized disk midplane coupled to a strongly magnetized corona, with a transition at vertical bar z vertical bar similar to 2H. The saturated alpha similar or equal to 0.01-0.02. A two-point correlation function analysis reveals that the central 4H of the disk is dominated by small-scale turbulence that is statistically similar to unstratified disk models, while the coronal magnetic fields are correlated on scales similar to 10H. Nevertheless angular momentum transport through the corona is small. A study of magnetic field loops in the corona reveals few open field lines and predominantly toroidal loops with a characteristic distance between footpoints that is similar to H. Finally, we find quasi-periodic oscillations with characteristic timescale similar to 30 Omega(-1) in the magnetic field energy density. These oscillations are correlated with oscillations in the mean azimuthal field; we present a phenomenological, alpha-dynamo model that captures most aspects of the oscillations.