  We investigate the launching mechanism of relativistic jets from black hole
sources, in particular the strong winds from the surrounding accretion disk.
Numerical investigations of the disk wind launching - the simulation of the
accretion-ejection transition - have so far almost only been done for
non-relativistic systems. From these simulations we know that resistivity, or
magnetic diffusivity, plays an important role for the launching process. Here,
we extend this treatment to general relativistic magnetohydrodynamics (GR-MHD)
applying the resistive GR-MHD code rHARM. Our model setup considers a thin
accretion disk threaded by a large-scale open magnetic field. We run a series
of simulations with different Kerr parameter, field strength and diffusivity
level. Indeed we find strong disk winds with, however, mildly relativistic
speed, the latter most probably due to our limited computational domain.
Further, we find that magnetic diffusivity lowers the efficiency of accretion
and ejection, as it weakens the efficiency of the magnetic lever arm of the
disk wind. As major driving force of the disk wind we disentangle the toroidal
magnetic field pressure gradient, however,magneto-centrifugal driving may also
contribute. Black hole rotation in our simulations suppresses the accretion
rate due to an enhanced toroidal magnetic field pressure that seems to be
induced by frame-dragging. Comparing the energy fluxes from the
Blandford-Znajek-driven central spine and the surrounding disk wind, we find
that the total electromagnetic energy flux is dominated by the total matter
energy flux of the disk wind (by a factor 20). The kinetic energy flux of the
matter outflow is comparatively small and comparable to the Blandford-Znajek
electromagnetic energy flux.
