The Observation Of Ionospheric D-layer Based On The Multi-station Lightning Detection System

It suffers great difficulties in remote sensing of the lower ionosphere by using conventional sounding methods. For the lower electron densities of ionospheric D layer, ionosonde (known as Swept-frequency pulse sounding method) cannot receive any echo at the lower frequency, ISR have a bad efficiency to measure the lower electron density region. However, Lightning have a strong radiates focus on the band of VLF(3-30kHz) and ELF(3-3000Hz), which could be reflected by the ionospheric D-layer and by the ground, thus propagates in a waveguide cavity between these two boundary. The sferics emitted by lightning and reflected by D-layer could be observed at the ground, which waveforms contains a greats deal of information of D-layer. At present, techniques utilizing the powerful very low frequency(VLF) radiation emitted by lightning discharges to sense the ionospheric D layer were under developing.In this study, we introduced and established a lightning based detection network to continuously record the lightning events and sound the fluctuations of ionospheric D layer by retrieve the virtual reflection heights of lightning events during the life cycle of thunderstorm.Based on recorded VLF lightning return-stroke waveforms in several days’data, in2012, the daytime fluctuation of D layer was investigated. Our results indicate that during the daytime, the virtual D layer reflection height of VLF radiation emitted by lightning discharges was in the range of60-75km and the variation trend of ionopsheric D layer was consistent with changes of solar zenith angle. From correlation analysis results between D layer reflection heights and solar X-ray flux densities recorded by GOES satellite, the solar flares will cause significant modification of the lower ionopshere and the responding time tended to be3-4minutes.With our network basement, we will develop a long wave propagation model to deduce the electron densities of D-layer, and find evidences to prove the ionosphere perturbation by lightning events, and the splitting of D-layer in the future.