Initial Evaluation of the Fuji-Centered Lightning Monitoring (FULMO) Network Using Boltek LRX-1 Receivers in Central Japan

We constructed a two-dimensional lightning location network, FULMO (Fuji-centered Lightning Monitoring), from Boltek LRX-1 receivers around Mt. Fuji in central Japan. These receivers observe lightning electromagnetic waves mainly in the very low frequency and low frequency (VLF/LF) band, and locations are obtained by time-of-arrival. Performance was evaluated against the Japanese Lightning Detection Network (JLDN). With six operational stations, the relative detection efficiency was 52.6% for JLDN cloud-to-ground (CG) strokes and 22.6% for intracloud (IC) discharges; the median location difference for CG strokes was 1.60 km. The difference depended strongly on station geometry: 0.85 km where the largest angular gap between azimuthally adjacent stations, as seen from the discharge, was <180°, and 6.53 km where that gap was ≥180°, the smaller value corre-sponding to discharges inside the group. Five features of the LRX-1 specification limit research use: the catalog carries a systematic timing offset of −0.99898 s requiring correction before catalog matching; it provides no quality index for the azimuthal distribution of contributing stations; it records only four station identifiers per location although more can contribute, leaving that distri-bution unknown; it does not discriminate CG from IC discharges; and it gives no polarity. We rec-ommend that the manufacturer address these points.