Observations of bidirectional lightning leader initiation and development near positive leader channels

摘要

Based on the analysis of high-speed optical and electric field change data, we present three observed cases in which a naturally occurring bidirectional lightning leader initiated and developed in virgin air near a previous established positive leader channel. Twice a new leader formed near an upward propagating positive leader that had initiated from a tower during an upward flash and once a new leader formed near a downward propagating positive leader prior to a positive cloud-to-ground return stroke. There were clear and consistent behavioral differences between the positive and negative leader ends of the newly formed bidirectional leader, and the positive end grew more slowly than the negative end in each case. In all three cases, the negative end of the bipolar leader connected with the previously formed positive leader channel creating a new positive leader branch. These rare observations show the bidirectional nature of naturally occurring lightning and suggest that positive leaders can gain branches by connection with newly formed bipolar leaders.