Long‐range lightning geolocation using a VLF radio atmospheric waveform bank

Abstract

[1] Lightning discharges generate broadband electromagnetic pulses with a peak component in the very low frequency (VLF; 3-30 kHz) range. VLF waves propagate through the Earth-ionosphere waveguide with relatively low attenuation, enabling the detection of these radio atmospherics at great distances from the lightning discharge. A new technique of long-range (≤6000 km) global lightning geolocation via sferic detection is presented. This new technique catalogs the dominant variation in expected received waveforms in a set of waveform banks, which are then used to estimate the propagation distance and accurately determine the arrival time. Using three sensors in a trial network, this new technique is used to demonstrate a median accuracy of 1-4 km, depending on the time of day. An overall cloud-to-ground (CG) stroke detection efficiency between ∼40 and 60% is estimated by correlating individual lightning stroke events to data from the National Lightning Detection Network (NLDN). Additional events reported by the trial network are shown to have a tight spatial clustering to storm clusters identified by NLDN, suggesting that many of the unmatched events correspond to weak cloud-toground strokes, M components, or cloud pulses. Exploiting an empirical correlation between peak VLF field strength and peak current values reported by NLDN, we also provide unvalidated estimates of the peak current and lightning channel polarity. The trial network does not distinguish between cloud and ground discharges, so these peak current estimates only relate to an Earth-referenced channel current for the subset of reported events that are return strokes.

Refining the relationship between lightning and convective rainfall over the ocean

“…The minimum detection threshold is roughly 5-7 kA, a level at which intracloud strokes can be detected. Comparisons with NLDN data, however, show that LLSs predominantly sample CG flashes (roughly 80%) [Pessi et al, 2009;Said et al, 2010Said et al, , 2013.…”

“…In early May 2011 and again in November 2011, Vaisala implemented improved reprocessing algorithms that, coupled with the growing network and improved site calibration, dramatically increased DE and LA across all domains [Said et al, 2010]. DE was generally greater than 50% across the northern hemisphere at the start of 2011 and the region surrounding the Hawaiian Islands was the only area of deficiency across the northern hemisphere.…”

“…GLD360's CG stroke DE during the time window of this study is estimated to be 60-70% across the northern hemisphere [Said et al, 2010]. For individual strokes, GLD360 records the date, time (with millisecond precision), latitude, longitude, maximum current, and polarity.…”

“…GLD360 uses magnetic direction finding and time-of-arrival techniques to locate lightning [e.g., Cummins et al, 1998Cummins et al, , 2000. Furthermore, each sensor uses recognition algorithms to diagnose sferic waveform variations resulting from propagation over great distances through the Earth-Ionosphere waveguide, which provides a more accurate geo-location [Said et al, 2010]. Observations are transmitted to Vaisala's Network Control Center in Tucson, AZ for processing and then made available to the data user in near real time [Grogan and Demetriades, 2009].…”

Analysis of lightning outliers in the EUCLID network

“…Although they are the best methods for retrieving robust information of a networks' performance, they are quite labor intensive when used to acquire a large enough dataset for a statistically reliable output. Other methods exist, such as the intercomparison of different LLSs within regions of overlapping coverage (Said et al, 2010;Pohjola and Mäkelä, 2013;Poelman et al, 2013b). However, the main disadvantage of those studies is the assumption that one network is the ground truth.…”