Statistical study of low-latitude E-region irregularity occurrence rate based on Qujing VHF radar observations

Based on the Quing VHF radar (25.6°N, 103.7°E, magnetic latitude 16.1°N, magnetic longitude 177.0°E) measurements from 2016 to 2020, the morphological characteristic of low-latitude E-region field-aligned irregularities (FAIs) was reported in this work. Statistical results show that the occurrence of Qujing E-region irregularities highly depends on both season and local time. The occurrence rate of E-region FAIs peaks in the summer, with the lowest occurrence rates in autumn and winter, and primarily occurs at night. The Doppler spectrum suggests that the Qujing E-region FAI echoes are mainly characterized by type II echoes. Quantitative analysis of both the activity of the Es layer and E-region FAI structures was also conducted. It is found that the occurrence of low-latitude E-region FAIs is closely correlated with the enhanced electron density structures inherent in the local Es layers. Given the weak electric field at low and mid-latitudes, neutral winds controlling ion drift likely trigger gradient drift instability above the Es layer, leading to small-scale irregularities in Qujing. Further investigation is required to understand the influence of the medium-scale traveling ionospheric disturbance on the occurrence rate of ionosphere E-region FAIs in low latitudes.