Lower ionosphere is difficult to probe for conventional measurements, as its altitude range is too low for the satellite and too high for atmospheric balloons. Recently, an alternative method to study lower ionosphere is using lightning signatures. In this work，we investigate the daytime fluctuations of lower ionosphere by analyzing the time domain VLF/LF waveform emitted by Narrow Bipolar Events (NBEs), which were recorded by an eight-station lightning location network called Jianghuai-Area Sferic Array (JASA) for a systemic real-time monitoring of lower ionosphere. JASA has been developed in 2012 and improved as a real-time lightning location network since 2018. We analyze numerous thunderstorm-day data and the preliminary results show that the lower ionosphere virtual height descends linearly at a rate of 5.9 km/h during sunrise, whereas rises linearly at a rate of 8.6 km/h during sunset. Moreover, the lower ionosphere virtual height short-time fluctuation is significantly modulated by the solar radiations’ flux density recorded by GOES satellite and the lower ionosphere diurnal variation pattern exhibiting a significant asymmetry, indicating that electron production in the lower ionosphere is dominated by the effect of solar radiation accelerating the neutral atmospheric molecules