Morphological Characteristics of the Station-to-Trough ratio of the African Equatorial Ionization Anomaly (EIA) during the maximum phase of solar cycle 24

The latitudinal profiles of the total electron content (TEC) obtained from Global Navigation Satellite System (GNSS) receivers at 13 ground stations around 36-40° E longitude was used to study the variations of the African equatorial ionization anomaly (EIA). This study focuses on the analysis of the station-to-trough TEC ratio (TEC-STR), an important parameter for quantifying the strength of the EIA. Data used for the present study covered the period from January 2012-December 2015. Our results showed that the diurnal variation pattern of the TEC-STR at 36-40° E longitude is characterized by two remarkable peaks around the crests of the African EIA, one occurring in the post-midnight hours, around 0600 LT, and the other in the post-sunset hours, around 2200 LT. The amplitudes of the post-sunset peaks are generally higher than the amplitudes of the post-midnight peaks. The TEC-STR showed a semi-annual variation with maximum peak values occurring in the equinoctial months. However, the TEC-STR for the southern hemisphere recorded higher values during the December solstice, revealing the existence of winter anomaly, whereas the TEC-STR trend for the northern hemisphere does not show this effect. The TEC-STR in the post-sunset hours shows a clear dependence on solar activity, where its values increase with solar activity.