Daytime equatorial spread F (ESF) is not as common as nighttime ESF due to the presence of a highly conducting E‐layer during the daytime which counteracts the development of F‐layer plasma irregularities. This study presents two rare daytime ESF‐like events which occurred over an interval ∼2 h and were detected by the HF Doppler receiver located in Lagos (LAG: geographic: 3.27°E, 6.48°N; dip latitude −1.72°) and the Lowell Digisonde at Ilorin (ILR; 4.68°E, 8.50°N; dip latitude −1.25°), managed by Lowell GIRO Data Center (LGDC). Analysis of the first event revealed ∼30 min periodic oscillations in iso‐heights of ionospheric electron density. Shorter period (∼15 min) oscillations appeared simultaneously in HF Doppler measurements and these oscillations lasted nearly 3 h. Close inspection of the ionograms from ILR during this interval (1500–1800 UT) showed the occurrence of small‐scale spreading in the F‐layer trace which varied in altitude as the disturbance progressed. Computation of the linear growth rate of the collisional Rayleigh‐Taylor instability showed that the plasma instability was seeded by a traveling ionospheric disturbance (TID). The characteristics of the second event suggest that horizontal stratifications in plasma density distribution at the reflecting ionospheric layer were responsible for the spread F traces in the ionograms. Analysis of GPS TEC data from Nigeria during these events revealed the presence of wave structures consistent with TIDs.

中文翻译：

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HF多普勒接收机和Digisonde检测到的白天赤道扩展F类异常

白天的赤道扩散F（ESF）不如夜间的ESF常见，这是因为白天存在高导电性的E层，从而抵消了F层血浆不规则性的发展。这项研究提出了两个罕见的白天类似于ESF的事件，它们发生在大约2小时的间隔内，并被位于拉各斯的HF多普勒接收机检测到（LAG：地理区域：3.27°E，6.48°N；倾角为-1.72°），而伊洛林（ILR; 4.68°E，8.50°N;倾角-1.25°）的Lowell Digisonde，由Lowell GIRO数据中心（LGDC）管理。对第一个事件的分析表明，电离层电子密度的等高约为30分钟的周期性振荡。在HF多普勒测量中同时出现了较短的周期（约15分钟），这些振荡持续了将近3小时。在此间隔（1500-1800 UT）期间，对ILR的电离图进行仔细检查后发现，在F层迹线中发生了小规模的扩展，随着干扰的进行，高度随高度而变化。碰撞瑞利-泰勒不稳定性的线性增长率的计算表明，等离子体不稳定性是由行进的电离层扰动（TID）引起的。第二次事件的特征表明，在反射电离层的血浆密度分布中的水平分层是造成电离图中的F迹线扩展的原因。在这些事件中对来自尼日利亚的GPS TEC数据进行的分析表明，存在与TID一致的波浪结构。碰撞瑞利-泰勒不稳定性的线性增长率的计算表明，等离子体不稳定性是由行进的电离层扰动（TID）引起的。第二次事件的特征表明，在反射电离层的血浆密度分布中的水平分层是造成电离图中的F迹线扩展的原因。在这些事件中对来自尼日利亚的GPS TEC数据进行的分析表明，存在与TID一致的波浪结构。碰撞瑞利-泰勒不稳定性的线性增长率的计算表明，等离子体不稳定性是由行进的电离层扰动（TID）引起的。第二次事件的特征表明，在反射电离层的血浆密度分布中的水平分层是造成电离图中的F迹线扩展的原因。在这些事件中对来自尼日利亚的GPS TEC数据进行的分析表明，存在与TID一致的波浪结构。