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tokens: of the angular velocity of the black hole. This could lead to quasi-periodic signatures in the observed radiation, especially if the radiation mechanism at the current sheet is to some extent beamed. However, in an actual accretion disc the flux tubes may be much more irregular and variable, leading to more stochasticity in the observed signal. The main dissipation mechanism is likely to be reconnection at these current sheets. Since the environment around the black hole is filled by soft optical/UV photons from the accretion disc, particles accelerated in the reconnection process will be quickly cooled through inverse Compton scatterings and may also initiate pair cascades on the soft photons. The reconnection outflow may be strongly Compton dragged, and the reconnection proceeds in a regime as described by Beloborodov ( 2017 ) where the spectrum is dominated by bulk Comptonization from the reconnection outflow and has a high-energy cut-off near the pair production threshold. To get an estimation of the dissipation rate in realistic systems, let us consider a typical Seyfert galaxy, MCG-6-30-15, which has a supermassive black hole of mass M = 2 × 10 6 M ⊙ , bolometric luminosity , and X-ray luminosity (Reynolds et al. 1997 ). Measuring B in terms of the characteristic field G (Phinney 1983 ), we get If the magnetic field near the black hole reaches a value B ∼ B Edd , then the amount of power dissipated due to the kink instability will be enough to account for all the X-ray emission. The kind of relatively strong magnetic field with small coherence length-scales may be a generic outcome of MRI in the accretion disc, or associated with hotspots on the accretion disc as the flux tubes emerge buoyantly similar to solar magnetosphere. As we have seen from GRMHD simulations, when the accretion disc is threaded by a strong net magnetic flux, it tends to become magnetically arrested and form a powerful jet (McKinney Blandford 2009 ; Avara, McKinney Reynolds 2016 ); however, in situations where the net magnetic flux is small, the disc magnetic field may be dominated by the locally amplified components. MRI and the subsequent buoyancy or gravitational instabilities can produce fields with alternating polarities (e.g. Davis, Stone Pessah 2010 ; Zhu Stone 2018 ); they may also be quite asymmetric. As these structures are fed to the black hole, we may see continuous flux tube inflation and kink instability happening on a much more stochastic basis. We have seen from the simulations that the kink instability tends to happen when the confinement from the surrounding field is strong; this confinement can be produced by magnetic field from currents in the outer disc, or a disc wind that exerts pressure towards the central axis region. We have so far approximated the black hole as a resistive membrane in a flat space–time model. Whether the other GR effects are important will be tested using a time-dependent, GR force-free code in the future. Meanwhile,