  We study the magnetospheric evolution of a non-accreting spinning black hole
(BH) with an initially inclined split monopole magnetic field by means of
three-dimensional general relativistic magnetohydrodynamics simulations. This
serves as a model for a neutron star (NS) collapse or a BH-NS merger remnant
after the inherited magnetosphere has settled into a split monopole field
creating a striped wind. We show that the initially inclined split monopolar
current sheet aligns over time with the BH equatorial plane. The inclination
angle evolves exponentially towards alignment, with an alignment timescale that
is inversely proportional to the square of the BH angular velocity, where
higher spin results in faster alignment. Furthermore, magnetic reconnection in
the current sheet leads to exponential decay of event horizon penetrating
magnetic flux with nearly the same timescale for all considered BH spins. In
addition, we present relations for the BH mass and spin in terms of the period
and alignment timescale of the striped wind. The explored scenario of a
rotating, aligning and reconnecting current sheet can potentially lead to
multimessenger electromagnetic counterparts to a gravitational wave event due
to the acceleration of particles powering high-energy radiation, plasmoid
mergers resulting in coherent radio signals, and pulsating emission due to the
initial misalignment of the BH magnetosphere.
