Study of the effect of propagation path on lightning-produced electromagnetic pulses based on LLN data

Lightning Location Network (LLN) has been used world-widely to report the peak current of a lightning return stroke based on the assumption that the peak current is proportional to the product of the amplitude of lightning-produced electromagnetic pulse (LEMP) and the source distance. However, this assumption is challenged by the data of rocketed-triggered return strokes. In this study, we propose a statistical approach for identifying the effect of earth path on the LEMP amplitude based on the LLN data. With the data from a Chinese regional LLN, it is found that the product of the LEMP amplitude and the source distance might be quite different at different distances for the same lightning stroke. A coefficient reflecting the effect of propagation path on the LEMP amplitude is defined. It is found that this path effect coefficient varied significantly at different distances and directions to a given sensor. Theoretical explanations for these findings are also explored. The findings are helpful to practically the correction of lightning peak current reported by a LLN, and theoretically the understanding of the rules of electromagnetic pulses propagating over the earth surfaces.