Quiet Time Ionopheric Irregularities Over the African Equatorial Ionization Anomaly Region

Abstract

This paper investigated variations of quiet time ionospheric irregularities over the African equatorial ionization anomaly using the rate of change of total electron content index. Irregularities were quantified in terms of percentage occurrence and examined along with parameter of the anomaly, mainly its strength and the asymmetry of the crests as well as equatorial electric field derived from the real‐time equatorial electric field model and meridional wind obtained from the horizontal wind model. Irregularities occurred from 19:30 to 03:00 LT with a time difference of 1 hr between both crests. The highest occurrences were registered in April: 91.67%, 75.00%, and 96.43% for the northern crest, trough, and southern crest, respectively. Seasonally, stronger anomaly (>20 total electron content unit) in addition to the highest equatorial electric field value in the dusk sector corresponded with the equinoctial higher occurrence rate in both hemispheres, while stronger meridional wind and farthest crests location accounted for the least occurrence in winter. The summer occurrence rate was favored by reduced meridional wind, smaller crests location, and late time of prereversal enhancement at the magnetic equator. There was a significant asymmetry in irregularities over the crests in both hemispheres with stronger and greater occurrence rate over the southern crest. Also, irregularities strength and occurrence rate were similar over the northern crest and trough in summer. In addition to dusk‐sector activity, irregularities occurred during postmidnight in summer. Simultaneous variations of irregularities at the crests and trough also highlighted the contribution of nonequatorial processes to their formation at the crests.

Comparison of ionospheric anomalies over African equatorial/low-latitude region with IRI-2016 model predictions during the maximum phase of solar cycle 24

“…The temporal and spatial resolution of the EIA maps obtained was 1 hour x 1 degree. We recall that there is a displacement of about 9 o between the magnetic equator and geographic equator within longitude 25 o -40 o E (Amaechi et al, 2020).…”

“…Both years fall within the maximum phase of SC-24 with mean observed annual solar flux of 122.76 and 146.54 solar flux unit (s.f.u), respectively. A day was deemed quiet if its Kp was lesser or equal to 3 (Amaechi et al, 2020;Fejer et al, 2008).…”

“…The meridional wind velocity was calculated using the technique described in Amaechi et al (2020). The estimation technique which takes into account the recommendation of Chartier et al (2015) is described in details in Kaab et al (2017).…”

Ground‐Based GNSS and C/NOFS Observations of Ionospheric Irregularities Over Africa: A Case Study of the 2013 St. Patrick’s Day Geomagnetic Storm

“…This was likely due to the smaller background ionization in the postsunset period on 17 March (Figure 5). Several researchers have stressed on the role of background ionization and its relation to irregularities formation (Aarons et al., 1981; Amaechi et al., 2020b; Tulasi Ram et al., 2006; Wernik et al., 1983). A contributing factor could have been the morphology of the EIA discussed in the past section.…”

“…Contrastingly, on 21 March, the formation of irregularities might have been promoted by the northward return of IMF Bz in the night (Figure 2, panel 2). The few studies on the relation between the anomaly and irregularities over Africa had focused on seasonal trends of variations in the strength of the anomaly and latitudinal extent of the crests (Amaechi et al., 2020b) as well as the values of CTR (Seba et al., 2018) during quiet time. These studies mainly revealed the asymmetry of the anomaly in winter and summer.…”