Vortices in Thin, Compressible, Unmagnetized Disks

We consider the formation and evolution of vortices in a hydrodynamicshearing-sheet model. The evolution is done numerically using a version of theZEUS code. Consistent with earlier results, an injected vorticity field evolvesinto a set of long-lived vortices, each of which has a radial extent comparableto the local scale height. But we also find that the resulting velocity fieldhas a positive shear stress, . This effect appearsonly at high resolution. The transport, which decays with time as t^-1/2,arises primarily because the vortices drive compressive motions. This resultsuggests a possible mechanism for angular momentum transport in low-ionizationdisks, with two important caveats: a mechanism must be found to injectvorticity into the disk, and the vortices must not decay rapidly due tothree-dimensional instabilities.Comment: 8 pages, 10 figures (high resolution figures available in ApJ electronic edition