Abstract This study investigates the quiet-time and storm-time variations of the African equatorial and low latitude ionosphere during 2009–2015. We obtained TEC observation data from four Global Navigation Satellite System (GNSS) stations over the African equatorial and low latitude, namely: Asab (ASAB, geographic coordinates 13.0°N, 42.65°E; geomagnetic coordinates 4.85°N, 114.34°E), Arba Minch University, (ARMI, 6.03°N, 37.56°E; 3.06°S, 109.29°E), Yamoussoukro (YKRO, 6.87°N, 5.24oW; 2.84°S, 67.41°E) and Mbarara (MBAR, 0.60°S, 30.74°E; 10.27°S, 102.36°E). Seven selected major Geomagnetic Storms (GSs) over solar cycle 24 were investigated and the responses of TEC and Rate of change of TEC Index (ROTI) as proxy for ionospheric irregularities to the storms were also studied. We recorded weaker ionospheric plasma density distributions around the magnetic equator (trough) than at the inner flank of the Equatorial Ionization Anomaly (EIA) crests: A clear evidence of EIA formation. Furthermore, hemispherical asymmetry was observed in the latitudinal distribution of TEC, with consistently higher distribution in the Northern Hemisphere (NH) than Southern Hemisphere (SH). TEC and ionospheric irregularities showed clear dependence on solar activity. Negative responses dominated GSs that occurred at night-time and positive effects for those that occurred during the daytime. The enhancement or inhibition of irregularities during GS is strongly dependent on the time of GS unfolding. As previously established, the daily maximum distribution of TEC at 1400–1600 LT and minimum at 0400–0600 LT were validated by this study, using long time (7 years) data. Seasonally, TEC showed semi-annual pattern of variations, with highest values in equinoxes, and lowest in solstices.

中文翻译：

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2009-2015年非洲赤道和低纬度电离层的安静时间和风暴时间变化

摘要 本研究调查了 2009-2015 年非洲赤道和低纬度电离层的安静时间和风暴时间变化。我们从非洲赤道和低纬度的四个全球导航卫星系统（GNSS）站获得了TEC观测数据，即：Asab（ASAB，地理坐标13.0°N，42.65°E；地磁坐标4.85°N，114.34°E），阿尔巴明奇大学，（ARMI，6.03°N，37.56°E；3.06°S，109.29°E），亚穆苏克罗（YKRO，6.87°N，5.24oW；2.84°S，67.41°E）和 Mbarara (MBAR.60R)南，30.74°E；10.27°S，102.36°E）。研究了太阳周期 24 中七次选定的主要地磁风暴 (GS)，还研究了 TEC 的响应和 TEC 指数变化率 (ROTI) 作为电离层不规则性对风暴的代表。我们记录到磁赤道（波谷）周围的电离层等离子体密度分布比赤道电离异常 (EIA) 波峰的内侧更弱：EIA 形成的明确证据。此外，在 TEC 的纬度分布中观察到半球不对称，北半球 (NH) 的分布始终高于南半球 (SH)。TEC 和电离层的不规则性显示出对太阳活动的明显依赖。负反应主导发生在夜间的 GS，而对发生在白天的 GS 产生积极影响。GS 期间不规则性的增强或抑制强烈依赖于 GS 展开的时间。如前所述，本研究验证了 TEC 在 1400-1600 LT 的每日最大分布和 0400-0600 LT 的最小分布，使用长时间（7 年）的数据。季节性地，TEC 显示出半年的变化模式，春分点的值最高，至点的值最低。