Location accuracy of VLF World-Wide Lightning Location (WWLL) network: Post-algorithm upgrade

An experimental VLF World-Wide Lightning Location (WWLL) network has been developed through collaborations with research institutions across the globe. The aim of the WWLL is to provide global real-time locations of lightning discharges, with > 50% CG flash detection efficiency and mean location accuracy of < 10 km. While these goals are essentially arbitrary, they do define a point where the WWLL network development can be judged a success, providing a breakpoint for a more stable operational mode. The current network includes 18 stations which cover much of the globe. As part of the initial testing phase of the WWLL the network operated in a simple mode, sending the station trigger times into a central processing point rather than making use of the sferic Time of Group Arrival (TOGA). In this paper the location accuracy of the post-TOGA algorithm WWLL network (after 1 August 2003) is characterised, providing estimates of the globally varying location accuracy for this network configuration which range over 1.9-19 km, with the global median being 2.9 km, and the global mean 3.4 km. The introduction of the TOGA algorithm has significantly improved the location accuracies. The detection efficiency of the WWLL is also considered. In the selected region the WWLL detected similar to 13% of the total lightning, suggesting a similar to 26% CG detection efficiency and a similar to 10% IC detection efficiency. Based on a comparison between all WWLL good lightning locations in February-April 2004, and the activity levels expected from satellite observations we estimate that the WWLL is currently detecting similar to 2% of the global total lightning, providing good locations for similar to 5% of global CG activity. The existing WWLL network is capable of providing real-time positions of global thunderstorm locations in its current form.