资源环境科技发展态势分析平台

The lightning sferic has been shown to be a valuable radio signal for detecting perturbations of the lower ionosphere caused by the lightning activity itself and by other terrestrial and space events (Shao et al., 2012, https://doi.org/10.1038/ngeo1668). Adding to many existing methods, we have recently proposed an improved ray theory (RT) model for investigating the lightning sferic transmission in the Earth-ionosphere waveguide (Qin et al., 2017, https://doi.org/10.1002/2016JD025599). In the present study, a further modification to the RT model was made to increase its accuracy in modeling the lightning sferic in a broader frequency band and a larger distance range. The modification included two aspects: a new incident angle finding technique and a novel method for deriving the high-order hop series. To quantitatively evaluate the effectiveness of the modification, a comparative study of this modified RT model with its previous version and the full-wave finite difference time domain model was carried out. The results showed that this modified RT model did better than its previous version and was in close agreement with the full-wave finite difference time domain method in modeling the lightning sferic in frequencies bands lower to 3, 5, and 7kHz for distances up to 500, 800, and 1,000km, respectively.