Propagation Characteristics of Lightning-Generated Whistlers in the Ionosphere: Statistical and Simulation-Based Analysis

Abstract

Lightning-generated whistlers (LGWs) are electromagnetic waves in the very-low-frequency band generated by lightning and propagate in the ionosphere. LGWs are an inexpensive ionospheric detection medium that can be used to reconstruct ionospheric electron density based on their dispersion characteristics. The propagation characteristics of LGWs determine their propagation paths in the ionosphere, and the correct calculation of these paths is a prerequisite for electron density inversion. Here the observations from the China Seismo-Electromagnetic Satellite in broad areas at about 500 km altitude are used to perform wave vector direction statistics and propagation characteristics analysis for fractional-hop whistlers that propagate from the Earth to the spacecraft. The propagation characteristics of whistlers are analyzed and distinguished using observational statistics of wave vector directions and simulation based on the finite difference time domain model. The results indicate that the wave normal angles of whistlers in low latitudes are significantly larger than those in mid latitudes. Low-latitude whistlers preferentially propagate obliquely outward in the magnetic meridian plane in a nonducted mode in the ionosphere. Mid-latitude whistlers may still propagate in a nonducted mode, even when their wave normal angles are relatively small. The wave normal angles of LGWs in the ionosphere show no significant longitudinal dependence and exhibit a clear latitudinal distribution pattern. The LGWs wave vector exhibits minimal vertical deviation at low and high latitudes, with significantly larger deviations near 30°N mid-latitudes. This paper reveals the propagation characteristics of LGWs in the ionosphere through observations, statistics, and simulation.