Initial Steps for a System to Monitor Space Weather Effects on the Lower Ionosphere Using Global Lightning as a Probe Signal

Abstract:

Solar events and Sun-magnetosphere interactions can cause significant impacts on Earth’s ionosphere. Solar flares and Earth-impacting coronal mass ejections enhance ionization in the lower ionosphere, inhibiting radio wave propagation in the Earth-ionosphere waveguide (EIWG). This enhanced ionization is observed in specific locations by ionosondes, and VLF propagation studies have previously been performed to assess the impact of space weather on the EIWG. However, these studies are typically limited by small numbers of fixed VLF transmitters and receivers, e.g. MSK stations, and as such can only observe the region of the EIWG along the few propagation paths between transmitters and receivers.

Here, we use global lightning as a VLF source, and an existing lightning detection network as a receiver. The World Wide Lightning Detection Network (WWLLN) uses ~100 stations around the world to detect VLF sferics and locate associated lightning strokes. By mapping sferic propagation paths between lightning strokes and WWLLN stations, and considering how this distribution of paths changes during solar events, we can observe attenuation regions in the EIWG caused by space weather. By comparing these to existing global attenuation estimates (e.g. from the NOAA D-Region Absorption Prediction model) and ionograms, we can build a near-real-time monitor of the lower ionosphere with global coverage.