Low-frequency ionospheric sounding with Narrow Bipolar Event lightning radio emissions: energy-reflectivity spectrum

摘要

We analyze data on radio-reflection from the D-region of the lowerionosphere, retrieving the energy-reflection coefficient in the frequencyrange ~5–95 kHz. The data are the same as developed for a recentstudy of ionospheric-reflection height, and are based on recordings ofpowerful (multi-Gigawatt) radio emissions from a type of narrow (~10 μs) lightning discharge known as "Narrow Bipolar Events". Thesequential appearance of first the groundwave signal, and then theionospheric single-hop reflection signal, permits us to construct theenergy-reflection ratio. We infer the energy reflection's statisticalvariation with solar zenith angle, angle-of-incidence, frequency, andpropagation azimuth. There is also a marginally-significant response of theenergy reflectivity to solar X-ray flux density. Finally, we review therelationship of our results to previous published reports.