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.

中文翻译：

---

非洲赤道电离异常 (EIA) 区域的安静时间电离不规则性

本文利用总电子含量指数的变化率研究了非洲赤道电离异常上安静时间电离层不规则性的变化。不规则性以发生的百分比量化，并与异常的参数一起检查，主要是其强度和波峰的不对称性以及来自实时赤道电场模型的赤道电场和从水平风获得的子午风模型。不规则发生在 LT 的 19:30 到 03:00，两个波峰之间的时间差为 1 小时。4 月份的发生率最高：北峰、海槽和南峰分别为 91.67%、75.00% 和 96.43%。季节性，更强的异常（> 20 总电子含量单位）除黄昏扇区最高的赤道电场值外，对应于两个半球的春分较高的出现率，而较强的经向风和最远的波峰位置在冬季最少出现。夏季发生率受经向风减弱、波峰位置较小和磁赤道反转前增强时间晚等因素的影响。两半球波峰的不规则性存在明显的不对称性，南波峰的发生率和发生率更高。此外，夏季北部波峰和波谷的不规则强度和发生率相似。除了黄昏部门的活动外，夏季的午夜后也出现了异常情况。