D-layer fluctuations directly above a thunderstorm region detected by using time-domain LF/VLF waveforms

This paper presents ionospheric D-layer fluctuations measured with high time and spatial resolution by using time-domain very-low and low-frequency (VLF/LF) lightning waveforms detected several hundred kilometers away from lightning storms. The technique compares the amplitude and the time delay between the direct ground wave and the first-hop ionospheric reflection of the lightning signal to measure the apparent D-layer reflectivity and height. For a region of the D-layer over a nighttime thunderstorm, the ionospheric reflection height is elevated by ~ 5 km for a period of ~1.5 hours. After the height lowers to its original level, significant propagating fluctuations in the height are apparent for 2.5 hours. These perturbations will be studied in relation to radar and lightning measurements from the thunderstorm directly below the ionospheric region.