With the widespread availability of ground and space-based global navigation satellite system (GNSS) observables, continuous and long-term explorations of ionospheric variations have been made possible worldwide or on regional basis with improved accuracy. The Formosa Satellite Mission#3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) mission has a huge database of radio occultation (RO) soundings at regional and global scales with a high vertical resolution. Comparative studies between radio occultation, incoherent scatter radar and ionosonde observations indicate that COSMIC profiles agree well with ground measurements. The present paper investigates the ionospheric profiles over Africa using COSMIC data for the period from 2006 to 2017, representing almost a solar cycle year of study. The spatiotemporal variation of electron density confirms a hemispheric asymmetry among the equinoctial seasons and the solstice seasons during both low and moderate solar activity. Seasonal/winter anomaly manifestation is also clearly noticed in our observations with relatively high electron density during the winter solstice than the summer solstice. Moreover, the electron density over the region show apparent spatial and temporal variations identical to earlier ground-based ionospheric monitoring results over the African region. The outcomes from this study would strengthen the understanding of the ionospheric alterations and modelling activities in Africa, especially the areas with inadequate ground-based measuring instruments, hence, our results may complement the progress in global ionospheric modelling.

中文翻译：

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来自 FORMOSAT-3/COSMIC 无线电掩星的非洲电离层电子密度特征

随着地面和天基全球导航卫星系统 (GNSS) 可观测数据的广泛应用，电离层变化的持续和长期探索在全球或区域基础上以更高的精度成为可能。台塑卫星任务#3/气象、电离层和气候星座观测系统 (FORMOSAT-3/COSMIC) 任务拥有一个巨大的区域和全球尺度的无线电掩星 (RO) 探测数据库，具有高垂直分辨率。无线电掩星、非相干散射雷达和电离探空仪观测之间的比较研究表明，COSMIC 剖面与地面测量结果非常吻合。本论文使用 2006 年至 2017 年期间的 COSMIC 数据调查了非洲的电离层剖面，几乎代表了一个太阳周期研究年。电子密度的时空变化证实了在低太阳活动和中太阳活动期间春分季节和冬至季节之间的半球不对称性。在我们的观察中也清楚地注意到季节性/冬季异常表现，冬至比夏至电子密度相对较高。此外，该地区的电子密度显示出与非洲地区早期地面电离层监测结果相同的明显时空变化。这项研究的结果将加强对非洲电离层变化和建模活动的理解，特别是地面测量仪器不足的地区，因此，我们的结果可能会补充全球电离层建模的进展。