Asymmetry of the Equatorial Ionization Anomaly (EIA) over the African low-latitude region

The highest Total Electron Content (TEC) values occur around the crests of the equatorial ionization anomaly (EIA). These are potential sources of positioning and navigation errors in Global Navigation Satellite System (GNSS). The redistribution of plasma under the influence of zonal electric field and neutral wind results in the asymmetry of the EIA in both hemispheres. This in turn is a precursor of the generation of ionospheric irregularities. Understanding variations of the EIA is thus, of practical importance for the smooth operation of GNSS technologies which have found widespread applications in various endeavors including the aviation industry. This is more so over the African sector where there are few studies on variations of the EIA. Hence, this work investigated the asymmetry of the African EIA during quiet periods (Kp ≤ 3) of year 2013 and 2014. TEC data obtained from a chain of 23 GNSS receivers over longitude 25.0 - 40.2^o E were used to reconstruct the EIA. The area under the ionization versus latitude curve (Area) from the trough up to the crests, as well as the strength of the anomaly (S) and its asymmetry (A) were estimated. The Area was different in both hemispheres during all months except in July 2014. In addition, the anomaly was stronger in March - April and September - November 2013 as well as February - April and September - October 2014. Conversely, it was less asymmetric in February - April 2013 and June - August 2014. Seasonally, the area under the TEC versus latitude curve from the trough to the crest was higher in the northern hemisphere than the southern hemisphere in equinox and winter while the reverse was the case in summer. Furthermore, equinox had the strongest anomaly strength followed by winter then summer. Also in 2013, the anomaly was less asymmetric (0.184) in winter than in equinox (0.346) but more asymmetric in summer (0.431). Oppositely, in 2014 it was more asymmetric in winter (0.795) than equinox (0.563) and weaker in summer (0.303). These results provide insight into the behavior of electric field and neutral wind and can play a significant role in forecasting the occurrence of post sunset ionospheric irregularities over the African low-latitude sector.