Disk Winds Driven by Magnetorotational Instability and Dispersal of Protoplanetary Disks

By performing local three-dimensional MHD simulations of stratified accretion disks, we investigate disk winds driven by MHD turbulence. Initially weak vertical magnetic fields are effectively amplified by magnetorotational instability and winding due to differential rotation. Large-scale channel flows develop most effectively at 1.5-2 times the scale heights where the magnetic pressure is comparable to but slightly smaller than the gas pressure. The breakup of these channel flows drives structured disk winds by transporting the Poynting flux to the gas. These features are universally observed in the simulations of various initial fields. This disk wind process should play an essential role in the dynamical evaporation of protoplanetary disks. The breakup of channel flows also excites the momentum fluxes associated with Alfvénic and (magneto-)sonic waves toward the midplane, which possibly contribute to the sedimentation of small dust grains in protoplanetary disks.