Applications of a Lightning Energy Metric Using Satellite Instrumentation and Monte Carlo Simulations

The Geostationary Lightning Mapper (GLM) provides continuous measurements of lightning on a hemispheric scale that can be used in a variety of applications. In particular, an estimate of the electrical energy of a lightning discharge is provided. While rapid increases in lightning flash rate have been shown to be linked to severe weather, the use of electrical energy evolution in this context is still being investigated. GLM affords such investigations, but work remains to be done to understand this new measurement. We present details of a lightning energy metric, based on a relationship developed using GLM event energy and simulated lightning optical energy, which represents a portion of the total electrical energy dissipated by a lightning discharge. Lightning optical energy is simulated using a Monte Carlo model building on previous studies, including a realistic lightning channel based on source points from the North Alabama Lightning Mapping Array (NALMA), and a source amplitude scaled using VLF waveforms via the Huntsville Alabama Marx Meter Array (HAMMA). Further, the scattering medium in the model incorporates an inhomogeneous droplet concentration and size, representing observed thunderstorm microphysics, specifically height dependent liquid and ice water. The application of this energy metric is a case study of a thunderstorm that occurred during the GLM field campaign in 2017. For the duration of the thunderstorm, the GLM event energy is used to diagnose the lightning source optical energy. Throughout the thunderstorm lifecycle, the energy metric is compared with simulated optical output from observed lightning flashes, and the temporal evolution of the energy metric throughout the thunderstorm is evaluated.