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.

We present a multi-instrumental analysis of a 20-hour duration Mesoscale Convective System (MCS) over the northwestern Mediterranean sea on September 21, 2019, that produced 21 sprites recorded with a video camera, of which 19 (90$\%$) were dancing sprites. The asymmetric trailing stratiform MCS developed in strong convective conditions (3500 J kg$^{-1}$) and formed a large and persistent overshoot with several convective cores (up to 25,000 km$^2$ with cloud top temperature $<$ -66$^{\circ}$C). It exhibited a bow echo structure with a probable inverted charge dipole within the convective region before the main sprite production period and associated with a large decrease of the negative cloud-to-ground (CG) flash rate. The sprite producing positive cloud-to-ground (SP+CG) flashes mainly initiated at the edge of the convective line on the side of the stratiform region. The flashes propagated over long distances (up to $\sim$ 200 km) across it producing both positive and negative CG strokes. Some parent flashes initiated within the stratiform region close to convective structures and propagated reversely. The 19 dancing sprite events included 49 sequences, of which 46 (94$\%$) were associated with distinct SP+CG strokes and 3 with surges during the continuing current. An especially bright and wide sprite sequence was produced by three distinct SP+CG strokes that occurred within 3 ms and separated by 54 km. This sprite sequence could be classified as a new sprite category resembling to a â\euroœwallâ\euro? but structured in three groups, each associated with one of the +CG strokes, but not separated by the video imagery.