A negative cloud-to-ground lightning flash initiating at a high altitude and starting without classic preliminary breakdown pulses

Abstract

A special negative cloud-to-ground (-CG) flash imaged by a low frequency lightning mapping system is reported in this paper. This flash initiated at a high altitude of about 11 km. The initiation location is inferred to be the lower edge of the upper positive charge region. Both initial positive and negative leaders had downward propagations, but during the initial 500 ms the negative leader had little development. An important feature of this -CG flash is that it did not start with classic preliminary breakdown (PB) pulses; there were only a few very small and narrow (~1 μs) pulses during the initial 100 ms. The absence of PB pulses was a direct result of the inactive initial negative leader, which was caused by the high initiation altitude. We suggest that lightning flashes, including CG and intracloud flashes, initiating at high altitudes (roughly >10 km) mostly start without classic PB pulses.