Analyzing positive cloud-to-ground lightning flashes with two leader propagation types – with and without recoil leaders

Inhalt:
Positive cloud-to-ground lightning (+CGs) are still little studied, mainly due to their low occurrence compared to negative cloud-to-ground lightning (−CGs). However, +CGs can be more dangerous, as they have more intense peak currents and long-lasting continuing currents. Some +CG leaders exhibit barely visible channels and several recoil leaders (small bipolar and bidirectional plasma channels) constantly retracing these channels, while propagating towards the ground before the return stroke (RS). Others, however, are composed of a single bright channel and without the occurrence of recoil leaders (RLs). This study compared different physical characteristics of these two types of +CG leaders. It was observed that +CG leaders without RLs propagate much faster and have a peak current with an intensity twice as high, on average, than +CG leaders with RL. The duration of the continuing current (CC) is similar for both cases, however there is a slight tendency for longer CCs in +CGs with RLs. Cases of the same +CG event with both behaviors were also observed, where the leader responsible for the first RS propagated faster and without RLs, and the leader responsible for the second RS propagated slower and with several RLs, in another channel.