Geomagnetic and Solar Dependencies of Midlatitude E‐Region Irregularity Occurrence Rate: A Climatology Based on Wuhan VHF Radar Observations

Abstract 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 (E S ) 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 E S layer and field‐line‐integrated Pedersen conductivity 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.