Characterization and applications of VLF/LF source locations from lightning using the Huntsville Alabama Marx Meter Array

Arrays that detect and locate the four-dimensional spacetime positions of radiation sources from lightning have largely utilized sensors sensitive to the very high frequency (VHF) regime with similar to 15 km baselines or very low frequency/low frequency (VLF/LF) regime with similar to 100 km baselines. This paper details initial results from the newly developed Huntsville Alabama Marx Meter Array (HAMMA), consisting of Marx meters (electric field change meters) sensitive to a frequency band similar to 1 Hz to 400 kHz. The arrival time of HAMMA waveforms due to radiation sources from lightning are used to determine the spacetime position of these sources. The locations are compared with two well-documented and operational arrays, the National Lightning Detection Network (NLDN) and the North Alabama Lightning Mapping Array (NALMA). The standard deviation of the difference between HAMMA and NLDN locations of return strokes is 305 and 266 m in x and y, respectively, while the standard deviation of the difference between HAMMA and NALMA sources is 237, 226, and 688 m in x, y and z, respectively. We further show that NLDN intracloud locations differ in horizontal distance from the corresponding HAMMA locations by a median value of 479 m. In addition, we use HAMMA source locations to map several lightning flashes in the VLF/LF and show HAMMA sources largely map out the same electrical extent as VHF sources and provide unique insights to the properties of the discharges occurring. Finally, we show that VLF/LF sources can determine the leader polarity in several example flashes but not necessarily whether a flash comes to ground.