Photographic observations of streamers and steps in a cloud-to-air negative leader



A color photograph has been obtained of a negative lightning leader in clear air at 10.3 km altitude. The individual leader steps are resolved as relatively straight segments of at least ~200 m in length, between sharp kinks (nodes) in the channel. Each node is accompanied by a group of streamers of ~100 m in length. One node has an unconnected secondary leader with streamers at both ends. Lightning Mapping Array observations show that the leader was part of an intracloud (IC) flash. The observation shows that steps of negative leaders near 10 km altitude are an order of magnitude longer than values reported in the literature for negative leaders near sea level. Since negative leaders propagate at comparable velocities at low and high altitudes, stepping occurs at a lower rate in IC flashes, which can explain why RF emissions from IC flashes are more intermittent than those from cloud-to-ground flashes.