Global MHD Simulations of Magnetic 
         Reconnection in Accretion Disks and in Disk Corona

Ryoji Matsumoto, Yoshiaki Kato, and Mami Machida

We present the results of resistive MHD simulations of 
accretion disks around a star or a black hole. The initial
state is a torus threaded either by the dipole magnetic field
of the central object or toroidal magnetic fields. We assume
anomalous resistivity to incorporate the effects of magnetic
reconnection. Magnetorotational instability growing in the
disk creates numerous current sheets. Magnetic reconnection 
taking place inside the disk reproduces 1/f-like X-ray 
fluctuations observed in black hole candidates. Three-dimensional
MHD simulations of radiatively inefficient black hole accretion 
flows revealed that when dense blobs accrete, large-scale current 
sheets are formed in the innermost region of the disk. Magnetic
reconnection taking place in the current sheet generates X-ray 
flares known as X-ray shots. When magnetic loops connect the 
central object and the disk, twist injection from the
disk or from the central object leads to the inflation of the loop. 
Magnetic reconnection taking place inside the explanding magnetic
loops inject hot plasmoids into the growing magnetic tower. 
In this model, the Poynting flux transports energy along the 
magnetic tower. This mechanism can explain the formation of 
semi-relativistic jets around a neutron star and relativistic
Poynting flux dominated jets in black hole candidates.