Localization of individual lightning discharges via directional and temporal triangulation of sferic measurements at two distant sites

Abstract

Lightning discharges generate electromagnetic pulses, known as sferics, that propagate through the waveguide formed by the Earth and the ionosphere. The energy in the VLF band can propagate over great distances (∼10,000 km) with low loss (3 dB/Mm) and can therefore be detected far from the source lightning location. Using sferic measurements from VLF receivers at Palmer Station, Antarctica, and Vieques Island, Puerto Rico, the locations of lightning discharges from regions such as South America, North America, and Africa are triangulated. Both sferic arrival azimuth at the two receivers and the time of arrival difference between the receivers are used to find the best estimate of the lightning discharge location. Owing to the extremely wide separation of the two receivers, ambiguities sometimes result in pairing sferics detected at one site to their matching sferics detected at the other site. In these cases a best‐best estimate scheme is used. Simulation results indicate that for the two receivers considered here the most accurate location performance is in South America with an expected median location error of ∼75 km. The system has the worst performance due north of the Vieques Island site, with an expected median location error of ∼2000 km. Triangulation results for South America are shown for the period 7–10 September 2001. Results for 8 September 2001 are compared to cloud‐to‐ground lightning flashes detected by the National Lightning Detection Network. For this day, 49% of flashes were detected with a median error of about 200 km. Results are also compared to lightning discharges detected by the Lightning Imaging Sensor (LIS) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite. For a particular TRMM pass over South America, 20% of flashes detected by LIS were correctly located using the described technique, with a median error of 187 km. The event rate for a localized South American storm is also monitored and documented for the same 4‐day period.