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We report new global ideal MHD simulations for thin accretion disks (withthermal scale height H/R=0.1 and 0.05) threaded by net vertical magneticfields. Our computations span three orders of magnitude in radius, extend allthe way to the pole, and are evolved for more than one viscous time over theinner decade in radius. Static mesh refinement is used to properly resolve MRI.We find that:(1) inward accretion occurs mostly in the upper magneticallydominated regions of the disk, similar to the predictions from some previousanalytical work and the "coronal accretion" in previous GRMHD simulations.Rapid inflow in the upper layers combined with slow outflow at the midplanecreates strong $R\phi$ and $z\phi$ stresses in the mean field; the verticallyintegrated $\alpha\sim 0.5-1$ when the initial field has $\beta_{0}=10^3$ atthe midplane. (2) A quasi-static global field geometry is established in whichflux transport by inflows at the surface is balanced by turbulent diffusion.The field is strongly pinched inwards at the surface. A steady-stateadvection-diffusion model, with turbulent magnetic Prandtl number of orderunity, reproduces this geometry well. (3) Weak unsteady disk winds are launchedat $z/R\sim1$ with the Alfven radius $R_{A}/R_{0}\sim3$. Although the wind isepisodic, the time averaged properties are well described by steady windtheory. Wind is not efficient at transporting angular momentum. Even with$\beta_{0}=10^3$, only 5% of the angular momentum transport is driven by torquefrom the wind, and the wind mass flux from the inner decade of radius is only$\sim$ 0.4% of the mass accretion rate. With weaker fields or thinner disks,the wind contributes even less. (4) Most of the disk accretion is driven by the$R\phi$ stress from the MRI and global magnetic fields. Our simulations havemany applications to astrophysical accretion disk systems.

Global Evolution of an Accretion Disk with Net Vertical Field: Coronal Accretion, Flux Transport, and Disk Winds