Lightning location using the slow tails of sferics

Electromagnetic waves produced by lightning strikes, known as sferics, and their extremely low frequency components, known as slow tails, propagate across the Earth-ionosphere waveguide. The properties of the recorded time domain slow tail vary with the causative lightning strike's current moment, the waveguide's characteristics, and the distance of propagation. These variations allow us to approximate the location of a causal lightning strike by examining the corresponding sferic. Many methods require measurements from multiple stations; however, the goal of this work is to approximate the distance a sferic propagated using measurements from a single station. J. R. Wait developed an analytical model that describes the propagation of the slow tail along a uniform path in the Earth-ionosphere waveguide. We examine different source functions and apply them to Wait's propagation model in order to ascertain a new and more accurate method for modeling slow tails while improving the accuracy of locating lightning using a single station. Further, we expand the model to include sferics propagating in a nonuniform ionosphere, i.e., crossing the day-night terminator. This new method provides improved correlation of computed slow tails to recorded ones, leading to a more accurate distance approximation for a larger set of sferics.