Parametric Modeling and Analysis of Lightning Sferic Waveforms for D-Region Remote Sensing

The ionosphere’s D-region and the Earth’s surface form what is known as the Earth-ionosphere waveguide (EIWG), facilitating long-distance propagation of very low frequency (VLF) signals. Lightning discharges emit broadband VLF radiation, known as sferics, which can travel thousands of miles in the EIWG with little degradation. The characteristics of lightning sferic waveforms are impacted by the D-region along the path of propagation between the source of the strike and the receiver. Thus, information about the state of the D-region can be extracted from received sferic waveforms, making them exceedingly useful for remote sensing of the D-region. In this work, we utilize an effective parameterized time-domain model of lightning sferics to aid in the analysis of the D-region. The model is applied to large VLF datasets containing thousands to millions of sferics obtained under a variety of ionospheric conditions. The resulting temporal and spatial variations in sferic parameters are analyzed and are shown to respond in conjunction with changes in ionospheric characteristics, including perturbations triggered by disturbances such as solar flares and eclipses.