Ionospheric D Region Disturbances due to FAC and LEP Associated With Three Severe Geomagnetic Storms as Observed by VLF Signals

Abstract

AbstractThe effects of one super and two intense storms on three European very low frequency (VLF) transmitter signals received at Algiers (Algeria) station, are presented. Two VLF transmitters (DHO and GQD) are located almost at the same mid‐latitude and third transmitter (NRK) at a high latitude, allowing us to study the latitudinal dependence of the storm effect on the VLF propagation. Two kind of ionospheric disturbances were considered: Direct effect of the field aligned currents (FACs) and the second concerning with the lightning‐induced electron precipitation (LEP) events. The FACs effect was clearly evident on the recorded signal amplitude during the daytime and nighttime. Our analysis of the short‐duration VLF perturbations due to LEP events showed that the ducted and non‐ducted LEPs are the majority of VLF perturbations and a small fraction of LEP events was associated with magnetospherically reflected waves on the high latitude transmitter path (NRK–Algiers). The coincident observation of LEP on the mid‐latitude transmitters (DHO and GQD) signals implies that the disturbance was large as much as the distance between the two transmitters (728 km). The modeling using Long‐Wave Propagation Capability (LWPC) code of LEP associated VLF perturbations considering Gaussian distribution of electron density enhancements, showed a decrease in the D‐region reference height from its usual value 87 km to 83.3 km for ducted LEP and 80.3 km for non‐ducted LEP event and that the non‐ducted event exhibited a wider disturbed region.