Shipborne LF‐VLF oceanic lightning observations and modeling. Issue 20 (23rd October 2015)

• Record Type: Journal Article
• Authors: Zoghzoghy, F. G.; Cohen, M. B.; Said, R. K.; Lehtinen, N. G.; Inan, U. S.
• Is Part Of: Journal of geophysical research. Volume 120:Issue 20(2015:Nov.)
• Page Start: 10, 890
• Page End: 10, 902
• Publication Date: 2015-10-23
• Subjects: lightning -- oceanic -- modeling -- statistics; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1002/2015JD023226
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Approximately 90% of natural lightning occurs over land, but recent observations, using Global Lightning Detection (GLD360) geolocation peak current estimates and satellite optical data, suggested that cloud‐to‐ground flashes are on average stronger over the ocean. We present initial statistics from a novel experiment using a Low Frequency (LF) magnetic field receiver system installed aboard the National Oceanic Atmospheric Agency (NOAA) Ronald W. Brown research vessel that allowed the detection of impulsive radio emissions from deep‐oceanic discharges at short distances. Thousands of LF waveforms were recorded, facilitating the comparison of oceanic waveforms to their land counterparts. A computationally efficient electromagnetic radiation model that accounts for propagation over lossy and curved ground is constructed and compared with previously published models. We include the effects of Earth curvature on LF ground wave propagation and quantify the effects of channel‐base current risetime, channel‐base current falltime, and return stroke speed on the radiated LF waveforms observed at a given distance. We compare simulation results to data and conclude that previously reported larger GLD360 peak current estimates over the ocean are unlikely to fully result from differences in channel‐base current risetime, falltime, or return stroke speed between ocean and land flashes. Key Points: Novel shipborne LF experiment to collect waveforms from deep ocean lightning Developed model to study the impact of return stroke parameters on ground wave Larger oceanic fields are unlikely due to changes in current rise, fall, or speed