Department of Space Science and Research Applications Development, Ethiopian Space Science and Technology Institute, Addis Ababa, Ethiopia.
Life Sci Space Res (Amst). 2020 May;25:18-27. doi: 10.1016/j.lssr.2020.02.004. Epub 2020 Feb 21.
As a result of the complex and typical behavior of the earth's magnetic field, the high latitude ionospheric parameters (such as the Vertical Total Electron Content, VTEC) are very dynamic. Thus, this study mainly focuses on the pattern of variation of the VTEC inferred from the GPS, IRI 2016, IRI-Plas 2017 and NeQuick 2 with different height over Antarctica during 2011-2017. It has been shown that the GPS-derived (GPS VTEC) and modelled (IRI 2016, IRI-Plas 2017 and NeQuick 2) VTEC do not show significant variations in the hourly values. This shows that the solar irradiance mostly responsible for the ionization of neutral molecules in the earth's upper atmosphere does not show significant hourly variation in the region. Moreover, the GPS VTEC values are larger than the modelled values on most of the hours with the highest Root-Mean-Square Deviations, RMSD (close to 14 TECU) resulting from underestimation of the VTEC by the IRI 2016 model being observed in the March equinox in 2014. On the other hand, relatively small RMSDs (less than 1 TECU) are observed on most of the hours in using all models, demonstrating that the models' performance is good with the NeQuick 2 model showing the best followed by the IRI-Plas 2017. Similar and smooth VTEC variation patterns are also observed in the bottom-side, topside and plasmaspheric layers during both the high and low solar activity years. This shows the TEC variation does not have significant impact on the signal propagated through the ionosphere in the polar region. Besides, the highest and lowest contributions of the TEC have been seen in the topside and plasmaspheric layers, respectively. The topside TEC contribution generally increases when the solar activity (or solar irradiance) increases; while, the plasmaspheric TEC contribution enhances when the solar activity (or solar irradiance) drops. Moreover, the largest bottom-side contribution is observed in the December solstice during 2014-2017.
由于地球磁场的复杂和典型行为，高纬电离层参数（如垂直总电子含量，VTEC）非常动态。因此，本研究主要集中在 2011-2017 年期间从 GPS、IRI 2016、IRI-Plas 2017 和 NeQuick 2 推断出的不同高度的南极 VTEC 变化模式。结果表明，GPS 衍生的（GPS VTEC）和建模的（IRI 2016、IRI-Plas 2017 和 NeQuick 2）VTEC 在小时值上没有明显变化。这表明，太阳辐射主要负责地球高层大气中性分子的电离，在该区域没有明显的小时变化。此外，在大多数小时内，GPS VTEC 值大于建模值，最高的均方根偏差（RMSD，接近 14 TECU）是由于 IRI 2016 模型对 VTEC 的低估，这种情况在 2014 年 3 月春分期间观察到。另一方面，在使用所有模型的大多数小时内，观察到相对较小的 RMSD（小于 1 TECU），这表明模型的性能良好，NeQuick 2 模型表现最好，其次是 IRI-Plas 2017。在高和低太阳活动年份，在底部、顶部和等离子体层中也观察到相似且平滑的 VTEC 变化模式。这表明 TEC 变化对极区中通过电离层传播的信号没有显著影响。此外，在顶部和等离子体层中分别观察到 TEC 的最高和最低贡献。当太阳活动（或太阳辐射）增加时，顶部 TEC 的贡献通常会增加；而当太阳活动（或太阳辐射）下降时，等离子体 TEC 的贡献会增强。此外，在 2014-2017 年期间的 12 月至日期间观察到最大的底部贡献。
