A comparison of the VLF waveform and optical emissions using ground based and spaced based lightning detection methods

With the launch of the Geostationary Lightning Mapper (GLM), high fidelity measurements of total lightning will be provided on a hemispheric domain by detecting optical emission from lightning from space. The fundamental measurement provided by GLM is a group, which is roughly analogous to a stroke. These are then congregated into flashes using spatial and temporal constraints. While current research using flash level data to relate lightning activity to severe weather has yielded important results, there remains more dynamic aspects of the data to exploit. Because stroke level data is the fundamental measurement, it is more consistent across many differing sensors when compared to flash level data. This allows for a more accurate comparison of different lightning detection methods. In order to better understand the type of measurements GLM will provide, we present initial work relating space based optical measurements to ground based VLF networks. Using the Lightning Imaging Sensor (LIS) and Huntsville Alabama Marx Meter Array (HAMMA), we explore the relationship between various characteristics of VLF waveforms and optical emission. Since GLM is largely based on LIS, this provides a way to understand the type of measurements GLM will provide prior to launch. Individual discharges, both IC pulses and CG strokes, detected by HAMMA are compared to LIS groups, and a relationship between various parameters such as rise time, pulse width, pulse duration and amplitude are used to determine when optical emission is detectable from space. Preliminary results show larger pulse widths, larger rise times, larger durations and larger heights are coincident with a LIS group occurrence for IC pulses, while for CG strokes larger rise times, larger durations, larger electric field changes and larger heights are coincident with a LIS group occurrence. Thus, the amplitude of the pulse and the height of the pulse inside the cloud are the most important factors in predicting if a LIS group will occur. Multiple pulses within the timeframe of a LIS group are also significant in light production, and have an additive effect. Because LIS is in low-earth orbit, time continuous measurements over a storm lifetime are not available. Hence, the comparison between LIS and HAMMA is used to build a logistic regression model to predict when optical emission will occur as a storm evolves. This model is applied to an example storm to understand how optical emission at a stroke level evolves with changing storm dynamics.