  By constructing a global model based on 3D local magnetohydrodynamical (MHD)
simulations, we show that the disk wind driven by magnetorotational instability
(MRI) plays a significant role in the dispersal of the gas component of
proto-planetary disks. Because the mass loss time scale by the MRI-driven disk
winds is proportional to the local Keplerian rotation period, a gas disk
dynamically evaporates from the inner region with possibly creating a gradually
expanding inner hole, while a sizable amount of the gas remains in the outer
region. The disk wind is highly time-dependent with quasi-periodicity of
several times Keplerian rotation period at each radius, which will be observed
as time-variability of protostar-protoplanetary disk systems. These features
persistently hold even if a dead zone exists because the disk winds are driven
from the surface regions where ionizing cosmic rays and high energy photons can
penetrate. Moreover, the predicted inside-out clearing significantly suppresses
the infall of boulders to a central star and the Type I migration of
proto-planets which are favorable for the formation and survival of planets.
