2019ApJ...878....4I

Numerical simulations of 1D force-free magnetodynamics (FFMD) by Koide and Imamura showed details of the energy extraction mechanism around a rapidly spinning black hole under the force-free condition in the case of a radial magnetic surface along the equatorial plane. The energy is transported like a tsunami from the ergosphere and spreads to the outside. In this paper, we perform 1D FFMD simulations with nonradial magnetic surfaces along the equatorial plane, which are more general magnetic surface configurations. Using the results of simulations and analytic solutions of the steady-state force-free magnetic field, we find that, except in the case of a radial magnetic surface at infinity, the tsunami induced at the neighborhood of the horizon damps gradually and energy flux along the equatorial plane vanishes after a long period of time or at infinity. This suggests the energy extracted from the spinning black hole through the nonradial magnetic field is transported toward the high latitude around the axis of the black hole and is converted to the kinetic energy of the jet or outflow.