Performance Assessment of the World Wide Lightning Location Network (WWLLN), Using the Los Alamos Sferic Array (LASA) as Ground Truth

Abstract

The World Wide Lighting Location Network (WWLLN) locates lightning globally, using sparsely distributed very low frequency (VLF) detection stations. Due to WWLLN's detection at VLF (in this case ϳ10 kHz), the lightning signals from strong strokes can propagate up to ϳ10 4 km to WWLLN sensors and still be suitable for triggering a station. A systematic evaluation of the performance of WWLLN is undertaken, using a higher-frequency (0-500 kHz) detection array [the Los Alamos Sferic Array (LASA)] as a ground truth during an entire thunderstorm season in a geographically confined case study in Florida. It is found that (a) WWLLN stroke-detection efficiency rises sharply to several percent as the estimated lightning current amplitude surpasses ϳ30 kA; (b) WWLLN spatial accuracy is around 15 km, good enough to resolve convective-storm cells within a larger storm complex; (c) WWLLN is able to detect intracloud and cloudto-ground discharges with comparable efficiency, as long as the current is comparable; (d) WWLLN detects lightning-producing storms with high efficiency in every 3-h epoch; thus, WWLLN can be useful for locating deep convection for weather forecasting on 3-h update cycles; and (e) WWLLN detects a stroke count in each storm that is weakly proportional to the stroke count detected by LASA. Thus, to the extent that lightning rate can serve as a statistical proxy for rainfall, WWLLN may eventually provide rainfall-proxy data to be assimilated in 3-h forecast update cycles.

A comparison of lightning data provided by ZEUS and LINET networks over Western Europe

“…From the analysis of the time coincident events it was evident that ZEUS can also detect IC strokes, a fact considered very important for the detection of thunderstorm activity that is predominantly characterized by IC activity. A similar result was also found on the analysis of WWLLN data over Florida (Jacobson et al, 2006). From Table 1 it is evident that the percentage of IC strokes relative to the total number of strokes sensed by LINET is ∼57%, while for the coincident strokes it is only ∼35%, indicating thus that ZEUS detects IC with a reduced efficiency compared to CG strokes.…”

A European lightning density analysis using 5 years of ATDnet data

“…For example, the design of ATDnet means that it will predominantly detect the emissions from CG return strokes. However, VLF systems have been shown to detect a proportion of IC discharges, as observed in data obtained by the WWLLN (Jacobson et al, 2006). As yet unpublished results obtained by analysing ATDnet data appear to confirm that ATDnet also picks up a proportion of IC discharges, but with a reduced detection efficiency relative to CG flashes.…”

“…the very low frequency range, in which radio signals propagate over the horizon in the waveguide created by the Earth and ionosphere, in order to create a "long-range" network. Only a small number of such long-range networks exist at the time of writing, including the University of Washington WWLLN (Worldwide Lightning Location Network) system (Jacobson et al, 2006), the Vaisala GLD360 (Global Lightning Dataset location accuracy: ATDnet location uncertainties within the region enclosed by the network of sensors are of the order of a few kilometres, as opposed to a few hundred metres possible with LF/VHF and VLF/LF systems. The location uncertainty of ATDnet makes it suitable for identifying electrically active cells.…”

The European lightning location system EUCLID – Part 2: Observations

“…This has been done by Anderson and Klugmann (2014), presenting the observations made by the Met Office Arrival Time Difference Network (ATDnet) over Europe. However, ATDnet's observations contain, similar to other VLF networks, a certain fraction of cloud signals in addition to CG lightning (Jacobson et al, 2006;Poelman et al, 2013b), which has not been accounted for in their analysis. In addition, the spatial distribution of lightning, i.e., CG and cloud lightning, over Europe has been measured by the optical transient detector (OTD) onboard the Orbview-1/Microlab satellite (Christian et al, 2003).…”

“…As such, it is possible to retrieve not only the geographical and frequency distribution of lightning on a global scale (Jacobson et al, 2006;Keogh et al, 2006;Said et al, 2010Said et al, , 2013, but detailed information at the level of individual strokes or flashes as well by means of three-dimensional reconstruction of the development of the lightning channel as observed by present-day lightning mapping arrays (LMAs) (Rison et al, 1999;Thomas et al, 2004;van der Velde et al, 2013;Defer et al, 2015). Nevertheless, each LLS has its pros and cons.…”