Abstract: Lightning channel reactivation is intimately linked to channel decay and cutoff processes, yet the transition from a conductive plasma channel to a non-conductive state remains difficult to characterize. Due to limitations of existing observation techniques, numerical modeling is essential to elucidate the mechanisms of channel decay and reactivation. A self-sustained charge neutrality intra-cloud lightning parameterization model is used to simulate multiple intracloud lightnings in various tripolar thunderstorm charge environments. The channel cutoff threshold is systematically varied to investigate its impact on lightning development and reactivation.
Simulation results indicate that lightning development is highly correlated with the channel cutoff threshold. Lower cutoff thresholds (10^-3-10^-2 S·m^-1) produce flashes with longer durations, more complex branching, and higher reactivation initiation fields (more than 300 kV·m^-1). In this regime, the channel still persists even when the channel conductivity is extremely low. Consequently, a high reactivation initiation field (more than 300 kV·m^-1) is required to re-ionize the decayed channel. Under these conditions, fewer than 20 reactivation processes are observed, most of which are short attempts (less than 100 m) as the channel is nearly insulating. Specifically, the low residual conductivity impedes charge transport, thereby making re-breakdown difficult to achieve. In contrast, higher thresholds (1-10 S·m^-1) lead to flashes that are shorter in duration and exhibit significantly fewer branches. Under these conditions, the channel is cut off while still maintaining significant residual conductivity, effectively serving as a primed path for subsequent discharges. Consequently, the reactivation initiation field decreases to 10-120 kV·m^-1, whereas the reactivation frequency increases to several hundred events, with reactivated channel lengths often exceeding 200 m. The number of significant reactivation processes notably increases. Furthermore, increasing reactivation events along the main channel lead to a further accumulation of residual conductivity. When subsequent reactivation propagates along these existing paths, the re-breakdown electric field is lowered, which facilitates the long-distance propagation of reactivation.
These results indicate that the lightning development process is intimately related to the channel cutoff threshold: Higher cutoff thresholds result in earlier channel extinction and shorter flash durations, but leave higher residual conductivity, thereby favoring reactivation. Conversely, lower thresholds prolong lightning evolution and promote spatial extension, yet the diminished residual conductivity suppresses reactivation. Frequent reactivation facilitates charge transfer and mitigates electric field enhancement, whereas limited reactivation allows for greater charge accumulation and higher field intensities. Therefore, the lightning development is regulated by the interaction between channel conductivity and reactivation processes.