By using Wuhan VHF radar, we show the morphological features of E‐region field‐aligned irregularity (FAI) occurrence at Wuhan during 2015–2020. Statistical results present that E‐region FAI occurrence reaches a maximum after sunset in summer season. According to Doppler spectrum features, type‐2 irregularity is predominantly observed at Wuhan. In addition, we observed a remarkable correlation between E‐region FAI occurrence and geomagnetic activity, which includes periods of positive correlation and negative correlation depending on different geomagnetic conditions. The strong negative correlation also exists between E‐region FAI occurrence and solar activity. In our observed results, we find that E‐region FAI occurrence shows a strong linkage with local sporadic E (ES) layer. A quantitative analysis of linear theory of plasma instability in the E‐region at midlatitudes is also presented in our study. The calculated results of linear growth rate indicate the importance of plasma density gradient of local ES layer and field‐line‐integrated Pedersen conductivity ΣPE+F ${{\Sigma}}_{P}^{E+F}$ on the generation of E‐region FAI. The geomagnetic and solar variations of E‐region FAI occurrence are also discussed in this study, which show a dependence on the geomagnetic and solar variations of both meteor rate and medium‐scale traveling ionospheric disturbance occurrence.

In this work, the daytime E‐region field‐aligned irregularities (FAIs) observed by the Qujing (geographic 25.64°N, 103.70°E) Very High Frequency coherent backscatter radar was reported. The range spread and enhanced sporadic‐E layer (Es) during the same period of the unusual radar echoes were separately observed by two ionosondes located at the Huize and Qujing. The Huize (geographic 26.51°N, 103.61°E) ionosonde was roughly located underneath the radar scattering volume which measured enhanced and range spread Es layer during this period of the unusual radar echoes, indicating that the daytime E‐region FAIs were closely related to the localized density gradient that embedded within the coordinated Es layer. Fengyun‐4A (FY‐4A) satellite data show that a strong convective activity accompanied by gravity waves occurred near the radar scattering volume region. As a result, we proposed that the gravity waves driven by the convective activity in the lower atmosphere can modulate the Es layers and then generate the daytime FAIs through the polarization process.

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