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

摘要

An experimental Very Low Frequency (VLF) World-Wide Lightning LocationNetwork (WWLLN) has been developed through collaborations with researchinstitutions across the world, providing global real-time locations oflightning discharges. As of April 2006, the network included 25 stationsproviding coverage for much of the Earth. In this paper we examine thedetection efficiency of the WWLLN by comparing the locations from thisnetwork with lightning location data purchased from a commercial lightninglocation network operating in New Zealand. Our analysis confirms that WWLLNfavours high peak current return stroke lightning discharges, and thatdischarges with larger currents are observed by more stations across theglobal network. We then construct a first principles detection efficiencymodel to describe the WWLLN, combining calibration information for eachstation with theoretical modelling to describe the expected amplitudes ofthe VLF sferics observed by the network. This detection efficiency modelallows the prediction of the global variation in WWLLN lightning detection,and an estimate of the minimum CG return stroke peak current required totrigger 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 ofhigh peak-current lightning. For example, in 2005 about 12% of the globalelve-producing lightning will have been located by the network. Since thelightning-EMP which produce elves has a high mean rate (210 per minute) ithas the potential to significantly influence the ionosphere on regionalscales.