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

• Published in: Radio science Vol. 56; no. 7
• Main Authors: Jacobson, Abram R., Holzworth, Robert H., Brundell, James B.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-07-2021
• Subjects: Amplitudes; anisotropy; detection efficiency; Earth; Electric fields; Ionosphere; ionospheric reflection; Lightning; Noise propagation; Radio attenuation; Radio stations; Radio waves; transmission; Very Low Frequencies; very low frequency; Wave attenuation; Wave reflection; Waveguides
• ISSN: 0048-6604; 1944-799X
• DOI: 10.1029/2021RS007293

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.
Plain Language Summary
Lightning strokes emit radio waves of varying strength. The global lightning‐monitoring system known as the World Wide Lightning Location Network provides an opportunity to infer features of radio attenuation of these radio waves as they propagate from the lightning to the network sensors. Although we do not know the amplitude of individual lightning strokes, we can form ratio's of each stroke's signal between pairs of stations that detect and record the same stroke's signal. We investigate the use of such ratios to study the radio attenuation process in the waveguide formed between the Earth's conductive surface and the conductive ionosphere about 70–90 km above the surface. In particular, we are able to account for the difference between daytime and nighttime attenuation, using a physics‐based model of radio reflection from the ionosphere.
Key Points
Infer signal attenuation even without precise knowledge of the source strength
Model the night‐to‐day transition in very low frequency radio attenuation in Earth Ionosphere Waveguide
Model based on full‐wave calculation of Very Low Frequency reflection from underside of ionospheric D‐layer