ALBERT

Description: Localized disturbances within the altitude range of lower ionospheric D-region, related to precipitation of energetic electrons from radiation belts, causes perturbations of VLF signal propagation parameters during nocturnal conditions within Earth-ionosphere waveguide. Based upon Very Low Frequency (VLF) signal perturbations through the remote sensing technique, indirect conclusions regarding some of the features of such Localized Ionospheric Enhancements (LIEs) can be obtained. In this work, several dozens of Lightning-induced Electron Precipitation (LEP) type VLF signal perturbations were analyzed as case studies, with the goal to get insight into similarities and differences between related LIEs formed in mid-latitude lower ionosphere over the west and central European region, using VLF recordings from two ground-based receiving systems, stationed at the Institute of Physics Belgrade (Serbia). Inspected cases included LEP events from period 2003 – 2011, with notable amplitude and phase changes compared to unperturbed ionospheric conditions. As input data for numerical simulations, amplitude and phase perturbations monitored on signals emitted from major European and American transmitters, were used. Subionospheric VLF signal propagation was modeled using the LWPCv21 program routine, relying on Wait's theory and by employing parameters sharpness and reflection edge height, for nighttime Great Circle Path (GCP) sections. Obtained electron density height profile changes along observed GCPs according to Belgrade VLF data, place the size as main common feature of considered LIEs, as less than: 1000 km in length and 500 km in width, with significant differences regarding their internal structure and position.