Two propagation scenarios of isolated breakdown lightning processes in
failed negative cloud-to-ground flashes
Abstract
Isolated breakdown (IBD) process is a lightning phenomenon that was
rarely reported in the past. It is characterized by radiowave pulses
typical for preliminary breakdown before negative cloud-to-ground
flashes, which fail to evolve into return strokes. We identified 128 IBD
pulse trains in measurements collected in the Mediterranean by a
broadband receiver (0.005 – 37 MHz) in 2015 and 2018. By combining
these records with concurrent Lightning Mapping Array measurements of
very high frequency radiation (60 – 66 MHz) emitted by in-cloud
discharges we investigate the development of each discharge. We identify
two scenarios: either the discharges continue to propagate almost
horizontally for more than 150 ms (73%), or they disappear sooner,
typically within several tens of milliseconds (27%). Using numerical
modeling, we verify that a potential barrier inside the thundercloud
caused by a strong lower positive charge center could indeed block
further propagation of lightning leaders toward the ground.