Detection efficiency of the VLF World-Wide Lightning Location Network (WWLLN): initial case study

Abstract

Abstract. An experimental Very Low Frequency (VLF) World-Wide Lightning Location Network (WWLLN) has been developed through collaborations with research institutions across the world, providing global real-time locations of lightning discharges. As of April 2006, the network included 25 stations providing coverage for much of the Earth. In this paper we examine the detection efficiency of the WWLLN by comparing the locations from this network with lightning location data purchased from a commercial lightning location network operating in New Zealand. Our analysis confirms that WWLLN favours high peak current return stroke lightning discharges, and that discharges with larger currents are observed by more stations across the global network. We then construct a first principles detection efficiency model to describe the WWLLN, combining calibration information for each station with theoretical modelling to describe the expected amplitudes of the VLF sferics observed by the network. This detection efficiency model allows the prediction of the global variation in WWLLN lightning detection, and an estimate of the minimum CG return stroke peak current required to trigger the network. There are strong spatial variations across the globe, primarily due to station density and sensitivity.The WWLLN is currently best suited to study the occurrence and impacts of high peak-current lightning. For example, in 2005 about 12% of the global elve-producing lightning will have been located by the network. Since the lightning-EMP which produce elves has a high mean rate (210 per minute) it has the potential to significantly influence the ionosphere on regional scales.

Direct satellite observation of lightning-produced NO<sub>x</sub>

“…Consequently, we expect our DE to be lower by a factor of about 4 (for a IC/CG ratio of 3). One striking difference is that our estimated DE shows a clear land-ocean contrast, which is not visible in the estimate by Rodger et al (2006). This is probably related to a land-ocean contrast in the DE of WWLLN, which is expected, since VLF radio waves propagate with less attenuation over seawater than over land.…”

“…13 Rodger et al (2006) explicitely estimate the DE for CG flashes (though WWLLN also detects IC flashes with sufficient peak currents), while our climatological approach based on LIS/OTD results in an "effective" DE for total (IC+CG) flashes. Consequently, we expect our DE to be lower by a factor of about 4 (for a IC/CG ratio of 3).…”

“…on the flash type (cloud-to-ground vs. intra-cloud): WWLLN is primarily focussing on the detection of cloud-to-ground (CG) flashes with well-defined return stroke peak currents (Rodger et al, 2006). However, Jacobson et al, 2006, showed that WWLLN is also capable of detecting intra-cloud (IC) flashes with similar DE, as long as their peak current is sufficiently high.…”

“…Above this level, the DE is not increasing further (Jacobson et al, 2006;Rodger et al, 2006Rodger et al, , 2009.…”

Large-amplitude transmitter-associated and lightning-associated whistler waves in the Earth's inner plasmasphere atL< 2

“…A rigorous determination of the wave propagation direction cannot be made without simultaneous wave magnetic and electric field measurements, or a propagation analysis from multiple antennae, neither of which is available on STEREO. However, lightning flash data from the World Wide Lightning Location Network (WWLLN) [Rodger et al, 2006] indicate that the north magnetic footprint of both spacecraft passed through a large lightning storm during the time of observations for both STEREO A and STEREO B.…”