2- AND 3-D SIMULATIONS OF MAGNETOCENTRIFUGAL DISK-WINDS: ACCELERATION AND STABILITY RUBEN KRASNOPOLSKY The University of Chicago and University of Illinois at Urbana-Champaign E-mail: ruben@oddjob.uchicago.edu ZHI-YUN LI University of Virginia ROGER D. BLANDFORD California Institute of Technology Abstract. Protostellar jets and winds are probably driven magnetocentrifugally from the surface of accretion disks close to the central stellar objects. The exact launching conditions on the disk, such as the distributions of magnetic flux and mass ejection rate, are poorly known. They could be constrained from observations at large distances, provided that a robust model is available to link the observable properties of the jets and winds at the large distances to the conditions at the base of the flow. We describe a set of 2D axisymmetric simulations that are able to follow the acceleration and propagation of the wind from the disk surface to arbitrarily large distances. After a typical 2D flow reaches the steady state, we impose on it nonaxisymmetric perturbations and follow numerically its 3D evolution. We find that the wind reverts quickly to its initial axisymmetric state, with no indication of rapid growth of instabilities leading to flow disruption. Our calculations strengthen the case for the magnetocentrifugal jet and wind launching. 1. 2-D Simulations: Acceleration to Large Distances The magnetocentrifugal mechanism (Blandford and Payne, 1982) is a leading can- didate for producing the observed jets and outflows observed around young stellar objects. Fluid elements are lifted off and accelerated centrifugally along rapidly rotating field lines firmly anchored on an accretion disk. The field lines can enforce rigid rotation up to a point where the energies in the bulk flow motion and the magnetic field are comparable. Beyond that point, the field becomes increasingly toroidal, and its hoop stress is thought to be responsible for wind collimation and jet production. This model links observable properties of the jets to conditions near the disk surface, such as magnetic field strength, or the mass ejection rate. Constraining these parameters requires high resolution observations (e.g. Bacciotti et al., 2002; Bacciotti, 2003), together with flow solutions up to these observable distances. A flexible approach to determine the properties of both steady-state and un- steady winds is through time-dependent numerical simulations (e.g. Ouyed and Pudritz, 1997; Ustyugova et al., 1997; Bogovalov and Tsinganos, 1999; Krasno- Astrophysics and Space Science 287: 75–78, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.