Response of the Earth’s Lower Ionosphere to Solar Flares and Lightning-Induced Electron Precipitation Events by Analysis of VLF Signals: Similarities and Differences

Aleksandra Kolarski,Vladimir A Srećković,Zoran R Mijić

doi:10.3390/app12020582

Aleksandra Kolarski, Vladimir A Srećković + Show 1 more

Open Access

https://doi.org/10.3390/app12020582

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Abstract

The lower ionosphere influences the propagation of electromagnetic (EM) waves, satellite and also terrestrial (anthropic) signals at the time of intense perturbations and disturbances. Therefore, data and modelling of the perturbed lower ionosphere are crucial in various technological areas. An analysis of the lower ionospheric response induced by sudden events during daytime-solar flares and during night-time-lightning-induced electron precipitation was carried out. A case study of the solar flare event recorded on 7 September 2017 and lightning-induced electron precipitation event recorded on 16 November 2004 were used in this work. Sudden events induced changes in the ionosphere and, consequently, the electron density height profile. All data are recorded by Belgrade (BEL) radio station system and the model computation is used to obtain the ionospheric parameters induced by these sudden events. According to perturbed conditions, variation of estimated parameters, sharpness and reflection height differ for analysed cases. Data and results are useful for Earth observation, telecommunication and other applications in modern society.

Highlights

The ionosphere, as a huge layer of the atmosphere, has physical and chemical properties that depend on the incident radiation and local energetic processes [1,2]
Since disturbances of very low frequency (VLF) signals are a consequence of electron precipitation caused by atmospheric discharges, they are named as lightning-induced electron precipitation events (LEP)
Ionospheric conditions highly differ depending on the time of day when sudden disturbances occur, with a transition period between stable daytime and stable night-time ionospheric conditions, i.e., during dawn and sunset being especially challenging for modelling

Summary

Introduction

The ionosphere, as a huge layer of the atmosphere, has physical and chemical properties that depend on the incident radiation and local energetic processes [1,2]. During SFs, electromagnetic radiation within soft X-rays in a wavelength range of 0.1–0.8 nm, significantly oversteps the ionization of the Lyman-a spectral line 121.6 nm and cosmic rays, becoming a major source of ionization at a range of altitudes corresponding to the D region (50–90 km, same), causing enhanced ionization and absorption of the EM waves that propagate within the Earth-ionosphere waveguide [9,10]. Perturbations in very low frequency (VLF) propagation, known as trimpi events, can be explained by formation of such areas. Since disturbances of VLF signals are a consequence of electron precipitation caused by atmospheric discharges, they are named as lightning-induced electron precipitation events (LEP). Disturbances in propagation of VLF radio signals at the Belgrade station BEL (located at the Institute of Physics Belgrade (44.85◦ N, 20.38◦ E), Serbia) were observed and the model computation is used to obtain the atmosphere parameters induced by these sudden events. Variation of estimated parameters, sharpness and reflection height differ for the analysed cases

Methods

Conclusions and Perspectives