Two Possible Scenarios for the Formation of Category 1 Bipolar Lightning Flashes

We present and discuss the current and electric field waveforms associated with two upward bipolar lightning flashes that occurred at the Säntis Tower. According to the traditional classification of bipolar flashes, both observed flashes could be classified as Category 1 flashes. The first one belongs to the subcategory 1a in which the polarity reversal during the initial stage is associated with an in-cloud process, while the second one involves the sequential initiation of two opposite-polarity leaders from the tower.