High-speed video and electric field observation of a negative upward leader connecting a downward positive leader in a positive cloud-to-ground flash

It has been discussed in past papers if a positive leader propagates in a stepped fashion or not. Some studies attribute the electric field pulses of a positive leader before connecting ground in a positive cloud-to-ground flash as a manifestation of the stepping of the positive leader. Some authors say, however, that it may be due to the stepping of the negative upward connecting leader during its ascension towards the downward positive leader. In this work we present a well documented case of a positive cloud-to-ground flash that shows that the pulses observed in the electric field preceding the return stroke are due solely to the upward propagation of a negative connecting leader. This flash was recorded simultaneously by a fast electric field sensor and a high-speed camera in July 2012 in the Black Hills area of South Dakota.