Diurnal Variations of the Electron Density in the Nighttime Lower Ionosphere Derived From a Massive Data Set of Tweek Atmospherics

Tweek atmospherics are ELF/VLF pulse signals with frequency dispersion characteristics that originate from lightning discharges. Previous research has employed tweek atmospherics to examine long‐term trends in the lower ionosphere; however, their utility in capturing diurnal‐scale variations has been largely unexplored. Based on the machine learning method, we statistically study a massive data set of 48,395 first‐order tweeks and obtain the diurnal variations of the nighttime lower ionosphere with a time resolution of 15 min. The variation amplitude of the mean reflection height () in a single night could reach 7 km for the first‐order tweeks, with an electron density variation () of 2.5 cm −3 . By comparison with the ionosonde observations from Wallops Island station and the incoherent scatter radar (ISR) observations from Millstone Hill station, we find that the correlation between the tweek‐inferred lower ionosphere and the F2‐layer electron density varies systematically with geomagnetic activity. In addition, the state of the tweek‐derived lower ionosphere is also related to the E‐region ionosphere (110–130 km), suggesting the presence of localized coupling process in this altitude range. Moreover, the comparison provides independent validation of our inversion technique with tweek atmospherics and confirms its potential to build a fully automated monitoring system for the nighttime lower ionosphere.