LAUSR

Fast Antenna Lightning Mapping Array (FALMA), a low-frequency lightning mapping system comprising an array of fast antennas, was developed and established in Gifu, Japan, during the summer of 2017. Location results of two hybrid flashes and a cloud-to-ground flash comprising 11 return strokes (RSs) are described in detail in this paper. Results show that concurrent branches of stepped leaders can be readily resolved, and K changes and dart leaders with speeds up to 2.4 × 10 m/s are also well imaged. These results demonstrate that FALMA can reconstruct three-dimensional structures of lightning flashes with great details. Location accuracy of FALMA is estimated by comparing the located striking points of successive RSs in cloud-to-ground flashes. Results show that distances between successive RSs are mainly below 25 m, indicating exceptionally high location accuracy of FALMA. Plain Language Summary We have developed a lightning mapping system called Fast Antenna Lightning Mapping Array (FALMA). FALMA detects low-frequency radio waves produced by lightning discharges at multiple sites and can reconstruct 3-D structures of lightning flashes. Three lightning flashes are analyzed in detail in this paper, and animations of seven cases are provided in the supporting information. These results demonstrate that FALMA can show development of lightning discharges in great details and accuracy. Types and polarities of lightning discharges can also be determined by the recorded electric field change waveforms. FALMA is expected to become a unique tool for lightning and thunderstorm researches. Research studies of several topics are already underway based on the observation data in the summer of 2017.