Using the World Wide Lightning Location Network (WWLLN) to Study Very Low Frequency Transmission in the Earth-Ionosphere Waveguide: 1. Comparison With a Full-Wave Model

We investigate a novel way to quantify Very Low Frequency transmission in the Earth-Ionosphere Waveguide, using data from the World Wide Lightning Location Network (WWLLN). The lightning signals from intense and long-duration storm clusters are recorded at several stations. Any individual stroke amplitude is in principle unknown, so that the recorded electric field from that stroke varies semi-randomly from the recorded field due to other strokes from that storm cluster. Thus, it is not possible to straightforwardly infer the channel characteristics from a stroke recorded at a single station. However, if two stations record the signal from the same stroke, then the inter-station ratio of the recorded amplitude on the two fixed propagation paths is (in the absence of noise) independent of source power. We develop a procedure to provide information on time-variations in the waveguide transmission, using an approach based on ratios of amplitudes from pair of stations which record the same strokes. These amplitude-ratio data are then compared to an existing model of full-wave Very Low Frequency reflection from the underside of the ionosphere.