The Detection of Continuing Current in Lightning Using the Geostationary Lightning Mapper

Lightning with continuing current may have current durations that last for hundreds of milliseconds, resulting in continuous optical emission that coincides with the uninterrupted current flow. The space-based Geostationary Lightning Mapper (GLM) is an optical sensor that allows for the detection of continuous optical emission. In this study, the optical properties associated with GLM flashes over North Alabama are characterized as continuing current flashes based on current durations estimated from electrostatic measurements. The GLM optical attributes associated with each flash are utilized to train a logistic regression model to predict the presence of continuing current across the GLM field of view. GLM flashes with higher probabilities of continuing current tend to cover a longer distance, a brighter maximum optical energy, and a larger maximum area over the span of the continuous optical emission. The continuing current model has a probability of detection (POD) of about 78% and a false alarm rate (FARate) of about 6% in North Alabama. Assuming these scores are applicable to other regions, about 13.3% of flashes detected by GLM in 2018 contain continuing current. The spatial distribution of GLM flashes reveals that continuing current flashes tend to occur over oceanic areas, while seasonal and diurnal analyses show that continuing current flashes tend to occur during wintertime and nighttime storms, which is consistent with previous Lightning Imaging Sensor results. Additionally, if the flash is known to be a cloud-to-ground flash, the continuing current model has a POD of approximately 80% and a FARate of about 4%.