Global radiolocation in the lower ELF frequency band

Abstract

A system for recording large‐amplitude discrete extremely low frequency atmospherics (ELF “events” or “Q bursts”) produced by global lightning activity is described. The location of the source lightning flashes for some 261 events has been deduced from these data. In the data set, about 75% of the signals were produced by positive flashes and 25% were produced by negative flashes. The analysis technique depends on the fact that in the lower ELF band (5–45Hz), signals can be detected which have made multiple circulations of the globe. The range of the sources was found by modelling the data using a least squares fit to the complex wave impedance computed using the well‐established propagation theory applicable to the Earth‐ionosphere spherical‐shell waveguide. The source bearings were deduced from two orthogonal components of the magnetic field vector using the usual goniometric technique. The data show that the majority of the sources of ELF events are located in low‐latitude regions, an average of 7.4 Mm away from the observing station situated in the UK. The use of such a system to monitor worldwide thunderstorm activity, so far as this relates to ELF events observed in the band 5–45 Hz, is demonstrated.