On the Role of Continuing Currents in Lightning-Induced Fire Ignition

Lightning flashes are an important source of wildfires worldwide, contributing to the emission of trace gases to the atmosphere. Based on experiments and field observations, continuing currents in lightning have since a long time been proposed to play a significant role in the ignition of wildfires. However, simultaneous detections of optical and radio signals from fire-igniting lightning confirming the role of continuing currents in igniting wildfires are rare. In this work, we first analyze the optical signal of the lightning-ignited wildfires reported by the Geostationary Lightning Mapper over the Contiguous United States (CONUS) during the summer of 2018, and we then analyze the optical and the Extremely Low Frequency signal of a confirmed fire-igniting lightning flash in the Swiss Alps. Despite data uncertainties, we found that the probability of ignition of a lightning flash with Continuing Current (CC) lasting more than 10 ms is higher than that of cloud-to-ground lightning in CONUS. Finally, we confirm the existence of a long CC (lasting about 400 ms) associated with a long-lasting optical signal (lasting between 2 and 4 s) of a video-recorded fire-igniting lightning flash.

Automated summary

Lightning flashes with continuing currents have been proposed to play a significant role in igniting wildfires. This study analyzes the optical and radio signals of lightning-ignited wildfires in the United States during the summer of 2018, as well as a confirmed fire-igniting lightning flash in the Swiss Alps. The results suggest that lightning with continuing current has a higher probability of igniting wildfires, and the existence of long-lasting continuing currents and optical signals in a fire-igniting lightning flash is confirmed.