Stepped Leader Initiation Via Positive Streamer System Intensification
A stepped leader initiation mechanism is elaborated. This mechanism is based on the propagation properties of positive corona streamers deduced from laboratory experiments in which a 0.65 meter uniform field gap was employed. When the ambient electric field strength within a portion of a thundercloud exceeds roughly 3 × 105 V m−1, a positive streamer system, once initiated by corona from a hydrometeor, can be expected to intensify as it advances in the direction of the local electric field (toward negative space charge). Because the positive streamer system is charged conservative and expands as it propagates, the net result is the separation of a substantial quantity of charge in which negative charge is concentrated while the positive charge is dispersed. This effectively redistributes cloud negative space charge in a way that increases the ambient field strength in part of the discharge region. Under appropriate conditions a sequence of such discharges, each one operating in the enhanced field produced by its predecessor, can be regenerative, leading to dielectric breakdown over a distance of several meters and the beginning of a stepped leader. These results are significant in that a plausible link is provided between corona from hydrometeors and the transient production of the very intense and relatively long-range electric field required to initiate a stepped leader within a thundercloud.
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