ULF Electromagnetic Field in the Upper Ionosphere Excited by Lightning

Abstract

We examine excitation of ultralow frequency (ULF) electromagnetic waves by an atmospheric lightning stroke in the upper ionosphere and the role of the ionospheric Alfvén resonator (IAR) in this process. We have theoretically calculated with the developed numerical model the spatial and spectral structures of electromagnetic disturbance in the ULF frequency range 0.1–6.0 Hz excited by an atmospheric lightning stroke on the ground and at ionospheric altitudes. The frequency band under consideration comprises typical frequencies of the IAR and the ionospheric waveguide. The spectra of horizontal magnetic and electric components reveal a spectral multiband structure in the upper ionosphere. The form of spectra depends significantly on the horizontal distance ρ from the source: spectral peaks associated with the IAR are evident at ρ≤400 km, whereas at ρ≥1,000 km the spectral peaks (>4 Hz) corresponding to the ionospheric waveguide modes can be seen. The model predicts that a vertical electric discharge with the charge moment MQ=106 C·m produces at altitude 500 km and ρ = 40 km a pulse with electric and magnetic amplitudes of about 4 mV/m and 4 nT, correspondingly, and duration ∼0.2 s. The pulse amplitude decays rather slowly with distance ∝ρ−1. Detection of ULF response in the upper ionosphere to isolated intense lightning stroke by low‐orbiting satellites with magnetic or electric sensors onboard is quite feasible.

Experimental Evidence of a Link Between Lightning and Magnetic Field Fluctuations in the Upper Ionosphere Observed by Swarm

“…Typical time delay between the lightning occurrence and the satellite detection is 0.2–0.5 s, which is generally consistent with theoretical predictions by Mazur et al. (2018). Such time delays indicate that we observe here rather a direct propagation of lightning‐generated disturbance than effects of excitation of the IAR resonance, which would require a longer time scale.…”

“…Mazur et al. (2018) assume that the lightning axis is co‐aligned with the purely vertical magnetic field, which is a good approximation rather for polar regions, where nonetheless lightning appear much less frequently than at lower latitudes. At low‐latitudes, where the analyzed cases occurred, the Earth's main magnetic field lines are inclined with respect to the vertical direction and so also relative to the expected typical cloud‐ground discharge axis.…”

Electromagnetic Field in the Upper Ionosphere From ELF Ground‐Based Transmitter

“…As a theoretical foundation for the results of the satellite observations we have developed a numerical model. This multilayered horizontally homogeneous model with a realistic ionospheric vertical profile and a vertical geomagnetic field is similar to the model used for ULF observations in Fedorov et al (2016) and Mazur et al (2018).…”

Modeling ELF Electromagnetic Field in the Upper Ionosphere From Power Transmission Lines

“…We use the multilayered horizontally homogeneous model with vertical geomagnetic field B 0 (inclination I = ±90°), similar to the model presented in Mazur et al. (2018). We use the Cartesian coordinate system with the unit vectors of coordinate axes , and the z axis is directed vertically upward.…”