Azimuthal dependence of VLF propagation

摘要

The World Wide Lightning Location Network (WWLLN) is used to measure the normalized lightning electric field at three network stations in order to examine the sferic attenuation between the stroke and the station. The electric field measurements are normalized to the radiated very low frequency (VLF) stroke energy to allow direct comparisons of the many stroke-station paths seen by WWLLN. Comparing past theoretical results and models show that WWLLN observes a stronger dependence of VLF propagation on magnetic azimuth compared to past work. The average attenuation over the water of eastward-propagating sferics is found to be 1.13±0.35 dB/Mm during the day and 0.71±0.68 dB/Mm at night, with westward-propagating sferics having average attenuation rates of 2.98±0.68 dB/Mm and 2.66±0.39 dB/Mm for day and night, respectively. Key PointsWWLLN is used to measure VLF attenuation for oceanic sferic paths.Attenuation change with magnetic azimuth is examined and compared to theory.VLF sferic propagation is observed under day and night ionospheres.