A Modeling Framework for Estimating Ionospheric HF Absorption Produced by Solar Flares

Abstract

A solar flare is a sudden enhancement in the Sun's electromagnetic radiation, specifically in the EUV and X-ray wavebands of the solar spectrum, lasting for a few tens of minutes to several hours (Hansen & Kleczek, 1962;Rastogi et al., 1999;Siskind et al., 2017). The intensification of solar radiation during a solar flare enhances the plasma density via photoionization in the Earth's lower ionosphere (D and lower E-region,  E 60-105 km) (Davies, 1990). This sudden enhancement of electron density leads to an increase in ionospheric high-frequency (HF: 3-30 MHz) radio wave absorption that disrupts over-the-horizon (OTH) communication, commonly known as the Dellinger effect or shortwave fadeout (SWF) (Dellinger, 1937). A statistical study by DeMastus and Wood (1960) showed there is almost a one-to-one relationship between an earthward directed solar flare and the occurrence of SWF. More recent studies have shown how the duration and intensity of SWF depend on duration and peak intensity of the solar flare, location of the transmitter and receiver, frequency of the radio wave, and the background ionosphere (Chakraborty et al., 2018;Fiori et al., 2018). SWF impacts on HF radiowave propagation can have impacts on sensitive systems. For example, a recent study by Redmon et al. (2018) demonstrates solar flare driven impacts to emergency HF communications supporting humanitarian aid services in conjunction with Hurricane Irma relief efforts

Transient Response of Polar‐Cusp Ionosphere to an Interplanetary Shock

“…We see a sudden dip in the number of backscatter echoes and a jump in riometer HF absorption following the SI onset. The observations suggest an enhancement in ionospheric HF absorption phenomena (Chakraborty et al., 2018; Chakraborty, 2021; Chakraborty, Bake, et al., 2021; Fiori et al., 2018) driven by energetic particle precipitation following the SI onset. We observe an early response in SuperDARN with respect to the riometer and show a delay before reaching a maximum drop in backscatter count.…”

Use of Terrestrial High Frequency Signals in Riometer Data to Explore the Size of D‐Region Electron Density Enhancements

“…Shortly following a solar flare (∼8 min), Extreme Ultra‐Violet and X‐ray radiation enhance D‐region ionization, causing significant radio‐wave absorption, the levels of which depend on operating frequency, solar‐zenith angle, and the magnitude of the flare (Davies, 1990). SWF having both high occurrence rate per solar cycle (Fiori, Kumar, et al., 2022) and large area‐of‐effect implies that modeling is of great importance to HF communication and navigation systems (Chakraborty et al., 2021; Fiori, Chakraborty, & Nikitina, 2022).…”

Variation of Ionospheric Shortwave Absorption of the Extraordinary Wave

“…Ionospheric HF absorption has been a topic of interest for many years, and extensive research has been conducted on the topic. Over the years, many effects on the ionospheric absorption such as climatology (Siskind et al, 2015(Siskind et al, , 2017, geomagnetic activity (Märcz, F, 1976(Märcz, F, , 1988Jussila et al, 2004;Li et al, 2015;Rodger et al, 2007), solar flares (Berngardt et al, 2019;Chakraborty et al, 2021), are studied.…”

“…In the ionosphere, radio wave absorption is caused by the collision of electrons with other particles (Chen & Fejer, 1975). When an electron collides with neutrals or ions (primarily neutrals) under the influence of the field of an incident radio‐wave, energy is transferred from radio‐wave to heat energy and finally transferred to ions and other electrons via momentum transfer equation which is governed by the conservation of momentum, and thus High Frequency (HF) radio waves experience absorption (Chakraborty et al., 2021; Fiori et al., 2022; Mitra, 1974). The ionospheric HF absorption can significantly influence the strength of the received signal.…”