Mapping Irregularities in the Postsunset Equatorial Ionosphere With an Expanded Network of HF Beacons

Abstract

Background and MotivationOne of the most common manifestations of space weather is the spontaneous generation of broadband plasma density irregularities in the postsunset equatorial F-region ionosphere. The phenomenon, often referred to as equatorial spread F (ESF) because of the spreading it produces in ionogram traces (Booker & Wells, 1938), is attributed to interchange instability in the F region which can become unstably stratified with the cessation of photoionization. The connection between ESF and interchange instabilities was established by Woodman and La Hoz (1976) who were the first to render coherent backscatter radar profiles observed at the Jicamarca Radio Observatory in range-time-intensity (RTI) image format. Their images resembled numerical simulations of interchange instabilities in barium clouds (e.g., Ossakow, 1981). Earlier, working also at Jicamarca, Farley et al (1970) had established a causal relationship between the height of the F layer at sunset and the occurrence probability of ESF, a finding which is consistent with if not uniquely indicative of interchange instability. Later, true images of large-scale irregularities associated with ESF were observed with the ALTAIR radar on Kwajalein which can scan from horizon to horizon (Tsunoda et al., 1979). These, together with increasingly accurate and finely resolved numerical simulations, cemented the link between ESF and ionospheric interchange instability (see e.g.,

An Empirical Model of the Occurrence Rate of Low Latitude Post‐Sunset Plasma Irregularities Derived From CHAMP and Swarm Magnetic Observations

“…Since the EPD occurrence shows a large variability both in small-and large-longitudinal scales (e.g., Kil & Heelis, 1998a;Kil et al, 2009;Martinis et al, 2021;Singh et al, 1997;Stolle et al, 2008;Tsunoda et al, 2018;Tsunoda & White, 1981), predicting EPD occurrence becomes even more challenging. Now, it is fairly well understood that missing understanding of the spatio-temporal behavior of EPDs, that is, growth, zonal movement and decay of EPDs, along with the paucity of continuous measurements of ionospheric parameters is the cause for the challenge in predicting the day-to-day occurrence variability of EPDs (e.g., Das et al, 2021;Hysell et al, 2021;Li et al, 2021;Patra & Das, 2023).…”