Ionospheric Nighttime Enhancements in the Equatorial Region as Revealed by the Beidou Geostationary TEC Observations

Abstract Ionospheric electron density enhancement at nighttime has been widely studied in the past decades. However, the mechanisms of this anomalous nighttime enhancement are not fully understood. In this study, we took advantage of the fidelity of geostationary total electron contents (GEO TECs) combined with the observations from three equatorial ionosondes to examine the morphology of equatorial ionospheric nighttime enhancements in the Asian‐Australian sector. The equatorial ionospheric nighttime enhancements from GEO TECs during 2016–2018 can be characterized by three categories. Each of these categories showed similar seasonal variations, with the maximal occurrence in the equinoxes. Interestingly, there was a strong correlation between the pre‐reversal enhancement (PRE) of the eastward equatorial electric field and these three types of equatorial ionospheric nighttime enhancements that were mostly accompanied by PRE inferred from foF2 and h'F2 from ionograms around dusk. Nevertheless, the formations of equatorial ionospheric nighttime enhancements could be associated with other factors, such as the equatorial electric fields and neutral winds, as well as associated plasma transports. This study provides a new perspective to explore the variations and the underlying physical processes of ionospheric nighttime enhancements.