Abstract The lack of reliable global E-region electron density or conductivity measurements has hampered a detailed and quantitative understanding of the E-region electrodynamic processes. The characterization of the global E-region ionospheric irregularities as a function of local time, longitude, and season remains a great challenge. In this study, we evaluate the electron densities retrieved by Wu (2018) in the D and E regions using ground-based radar data and empirical models. Unlike in the conventional top-down retrieval methodology, the new approach avoids the Abel weighting function that carries substantial sensitivity to the electron density residuals from the F-region even after they have been corrected. The new technique uses a bottom-up approach in which the F-region contributions in the excess phase are more effectively removed compared to the Abel inversion, and hence more accurate electron density retrievals in D and E regions are determined. The results are compared and evaluated with two low and mid-latitude incoherent scatter radar observations - the Arecibo Observatory’s 430 MHz radar, located in Puerto Rico (18 ∘ N, 67 ∘ W) and the Millstone Hill Observatory’s 440 MHz radar, located in Massachusetts (42 ∘ N, 72 ∘ W). In addition, the results are also compared with two models - the International Reference Ionosphere model (IRI-2016) and the Faraday International Reference Ionosphere model (FIRI-2018) at these two locations. The comparison of electron density height profiles from GPS-RO retrievals at the two locations show good agreement with radar measurements, as well as the FIRI-2018 model predictions, especially at ∼ 85 - 100 km. The seasonal and diurnal climatology comparisons of GPS-RO retrieved electron density show good agreement with radar observations at both locations, and also reflect the influence of the solar cycle on E-region electron density. It is noticed that the GPS-RO background electron density at Millstone Hill increases by ∼ 20% at around 105 km from solar minimum to the maximum during cycle 24 which is in agreement with radar observations and FIRI-2018 model predictions.

中文翻译：

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使用雷达观测和模型对 D 区和 E 区进行自下而上 GPS-RO 电子密度反演的比较和评估

摘要 缺乏可靠的全局 E 区电子密度或电导率测量阻碍了对 E 区电动过程的详细和定量理解。将全球 E 区电离层不规则性表征为当地时间、经度和季节的函数仍然是一个巨大的挑战。在本研究中，我们使用陆基雷达数据和经验模型评估了 Wu (2018) 在 D 和 E 区域检索到的电子密度。与传统的自上而下的检索方法不同，新方法避免了 Abel 加权函数，该函数对 F 区域的电子密度残差具有相当大的敏感性，即使它们已被校正。新技术使用自下而上的方法，其中与 Abel 反演相比，可以更有效地去除多余相中的 F 区贡献，从而确定 D 和 E 区中更准确的电子密度反演。结果与两个低纬度和中纬度非相干散射雷达观测结果进行比较和评估 - 阿雷西博天文台位于波多黎各（18 ∘ N，67 ∘ W）的 430 MHz 雷达和位于马萨诸塞州的 Millstone Hill 天文台的 440 MHz 雷达(42 ∘ N, 72 ∘ W)。此外，还将结果与这两个位置的两个模型——国际参考电离层模型（IRI-2016）和法拉第国际参考电离层模型（FIRI-2018）进行了比较。两个位置的 GPS-RO 反演电子密度高度剖面的比较表明，与雷达测量以及 FIRI-2018 模型预测非常吻合，尤其是在 85 - 100 公里处。GPS-RO 反演电子密度的季节和昼夜气候比较表明，这两个位置的雷达观测结果吻合良好，也反映了太阳活动周期对 E 区电子密度的影响。注意到磨石山的 GPS-RO 背景电子密度在第 24 周期从太阳最小值到最大值约 105 公里处增加了约 20%，这与雷达观测和 FIRI-2018 模型预测一致。GPS-RO 反演电子密度的季节和昼夜气候比较表明，这两个位置的雷达观测结果吻合良好，也反映了太阳活动周期对 E 区电子密度的影响。注意到磨石山的 GPS-RO 背景电子密度在第 24 周期从太阳最小值到最大值约 105 公里处增加了约 20%，这与雷达观测和 FIRI-2018 模型预测一致。GPS-RO 反演电子密度的季节和昼夜气候比较表明，这两个位置的雷达观测结果吻合良好，也反映了太阳活动周期对 E 区电子密度的影响。注意到磨石山的 GPS-RO 背景电子密度在第 24 周期从太阳最小值到最大值约 105 公里处增加了约 20%，这与雷达观测和 FIRI-2018 模型预测一致。