Investigation of GLM detections of negative continuing currents observed by high-speed video and narrow-band 777 nm photometer

Lightning flashes with continuing currents are characterized by high energy transfer to ground that produces severe damage to electric power systems. Novel space-based optical lightning detection systems offer new possibilities to identify flashes with continuing currents. In this work, we analyze the Geostationary Lightning Mapper (GLM) detections of ten negative cloud-to-ground flashes observed from ground by a high-speed camera and a photometer. Results show that 10 out of 25 of the observed negative CG flashes produced continuing currents. In 6 out of 11 of the observed continuing currents, GLM provided more than four consecutive detections of events. The average duration of continuous detection of GLM events during continuing currents represents 10 % of the total duration of the continuing currents. The GLM detection limits compared with ground-based-optical instruments is related to the GLM sensitivity threshold. Additional Colombia Lightning Mapping Array data revealed that in-cloud positive leaders associated with the continuing currents propagate at low altitudes, corresponding to the midlevel negative charge region. The development of these leaders at low altitudes, along with weaker negative continuing currents levels compared to positive flashes, makes them challenging to detect by GLM. This work provides insights into the interpretation of space-based continuing currents optical detection.