Collaborative Research: Quantitative Analysis of Lightning's Multifaced Impact on the Ionosphere

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This award addresses fundamental questions about the impact of lightning discharges on the lower ionosphere (60-90 km). Lightning discharges are among the most powerful sources of electrostatic fields and electromagnetic radiation and are known to create significant disturbances in the lower ionosphere. Specifically, two well documented perturbations stem either from direct heating, known as Early/Fast (E/F) events, or from induced bombardment by energetic particles from the radiation belts, known as lightning-induced electron precipitation (LEP). The low ambient electron density of the lower ionosphere precludes direct measurement by standard radar techniques, hence observations of E/F and LEP events are made using remote sensing with Very Low Frequency (VLF, 3-30 kHz) waves from powerful communication transmitters. VLF signals reflect from the lower ionosphere and are perturbed in amplitude and phase when an ionospheric disturbance occurs along the path, thus allowing a form of continuous observation. Efforts to diagnose and understand the physics of disturbances have yielded largely qualitative results to date. This project will bring together two experts in ionospheric and magnetospheric processes to realize the full potential of VLF remote sensing. This project will enhance efforts to forecast navigation and communication outages due to lightning-induced disturbances. Early-career PIs at each institution will lead the project, which will also contribute to the support of several graduate students and a post-doctoral researcher. Unambiguous determination of the physics of ionospheric disturbances from VLF signal perturbations has been lacking due to the complex nature of VLF signal propagation and also the variability of lightning discharges. In this effort, the challenges to quantifying lightning-ionosphere coupling with VLF remote sensing by introducing the following innovations: 1. Strategic observations of ocean-based lightning and overlapping VLF transmitter paths. 2. Novel polarization and scattered field analysis from amplitude and phase in two channels.3. Quantifying the role of the lightning source spectrum in the ionospheric disturbance.4. Improvement of numerical codes for trans-ionospheric propagation and raytracing.