The Modeling of Lightning-Generated Sferics Observed Onboard a Ship at Sea

Abstract:

A newly developed large-wavelength numerical scattering simulator is incorporated into a propagation model for lightning-generated sferics in the very low frequency band (VLF, 3-30 kHz). In this case, with measurements taken onboard a ship at sea, the large wavelength scattering to be accounted for is produced by the ship itself. Previous analysis identified strong frequency-dependent scattering in the VLF band, a result that was used to imply that the scattering could affect ship-borne observations of lightning properties. This paper presents the results of VLF sferic propagation modeling that incorporates the long wavelength scattering in order to directly evaluate how the ship affects observations of lightning sferic rise-time, fall-time, peak value, and polarization (or direction of arrival). These results provide context for previous ship-bourne observations of lightning-generated sferics, which have been used to analyze why oceanic lightning appears to have larger peak currents than over-land lightning.