资源环境科技发展态势分析平台

Evidence of positive polarity dominated streamers preceding fast negative breakdown and of simultaneous positive and negative polarity streamer development in lightning initiation is reported. Observations of lightning initiation as fast negative breakdown have remained a puzzle because simulations of lightning initiation have shown that negative streamers are not produced in virgin air without simultaneous positive streamers. Here, we observe positive streamer development forms first or at least simultaneously with negative streamers. Further evidence comes from observations of mixed fast breakdown. The overall trajectory of the positive breakdown during such mixed events indicates that the positive streamers continuously propagate during the burst of strong negative breakdown. These observations indicate that even when negative streamers dominate the overall VHF emissions, both positive and negative streamers are propagating simultaneously from the initiation point. These findings on the structure and dynamics of fast breakdown provide key new insight to our understanding of lightning initiation.