Ionospheric topside $O^{+}$ diffusive flux is derived using Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation data, to investigate its global distribution and also its role in winter nighttime enhancement (WNE) of electron density. The flux of the winter hemisphere maintains downward throughout the night. It is much larger between $30°$ and $50°$ geomagnetic latitudes and keeps increasing until 22:00–00:00 LT. It peaks at $60°$W and $60°$E–$120°$E geographic longitudes during the December solstice, and at $180°$E during the June solstice. These features are similar to those of WNE in NmF2. Furthermore, the derived flux is applied as the upper boundary condition to run the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). The simulated spatial-temporal variations of WNE are consistent with the observations. The results indicate that downward plasma diffusion from the plasmasphere is the major mechanism of WNE, and the simulation quantifies its contribution.

中文翻译：

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冬季夜间电离层上部扩散通量和中纬度电子密度增强的全球分布


电离层上 $O^{+}$ 部漫射通量是使用星座气象、电离层和气候观测系统 （COSMIC） 射电掩星数据得出的，以研究其全球分布及其在冬季夜间电子密度增强 （WNE） 中的作用。冬季半球的通量在整个夜间保持向下。它在地磁纬度之间 $30°$ $50°$ 要大得多，并一直增加到 22：00–00：00 LT。它在 $60°$ 12 月至日的 W 和 $60°$ E-E $120°$ 地理经度处达到峰值，在 6 月至日期间在 $180°$ E 达到峰值。这些特征类似于 NmF2 中 WNE 的特征。此外，将推导的磁通量用作上边界条件来运行热层电离层电动力学一般环流模型 （TIEGCM）。模拟的 WNE 时空变化与观测结果一致。结果表明，等离子体从等离子体层向下扩散是 WNE 的主要机制，模拟量化了其贡献。