Quiet time ionopheric irregularities over  the African Equatorial Ionization Anomaly (EIA) region

This paper investigated variations of quiet time ionospheric irregularities over the African Equatorial Ionization Anomaly using the rate of change of TEC index (ROTI). Irregularities were quantified in terms of percentage occurrence and examined along with parameter of the Anomaly mainly its strength and asymmetry of the crests as well as equatorial electric field (EEF) derived from the real time equatorial electric field model and meridional wind obtained from the horizontal wind model. Irregularities occurred from 19:30 – 03:00 LT with a time difference of 1 hour 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 TECU) in addition to the highest EEF 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 was 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 over the crests and trough also highlighted the contribution of non equatorial processes to their formation at the crests.