Beyond bidirectional leaders: The unseen role of side discharges in lightning propagation
While bidirectional leaders have long been considered the primary driver of lightning development, recent observations reveal the critical yet overlooked role of side discharges -- needle-like negative breakdowns and nearby bidirectional leaders -- in sustaining and shaping lightning channels. Here, by integrating high-speed optical imaging with low-frequency lightning mapping data, we reveal that needle discharges dynamically reverse their breakdown polarity to act as connecting leaders during bidirectional leaders' approach. Their connection significantly enhances the luminosity of the positive leader channel, predominantly on one side from the connection point, backward-end or advancing-end. Such channel luminosity increases correlate with the different polarity of transferring charge, suggesting an unequal potential distribution of the lightning channel. Our findings challenge the traditional bidirectional leader model and establish an unbalanced lightning propagation framework, demonstrating that side discharges critically regulate lightning channel stability and branching.
Found an error? Please report to login@optimap.science.