Assessment of Cloud Lightning Detection by the U.S. National Lightning Detection Network using Video and Lightning Mapping Array Observations
The VHF LMA data provides a description of the spatial and temporal evolution of a flash. For flashes identified as IC discharges, we examined whether there was any correlation between the temporal and spatial behaviors of the LMA-reported VHF sources associated with a flash and low frequency IC pulses reported by the NLDN. Our results support the findings of previous studies that most of the reported cloud pulses occur during the initial breakdown period of a flash when channels (as defined by VHF sources) extend from the main negative to the upper positive charge region. Following the initial breakdown period, additional vertical channels may develop between the main negative and upper positive charge regions (as seen from VHF sources) during which the NLDN also reports some IC pulses. Finally, at later stages in a flash, the NLDN may report pulses with no associated VHF sources, indicating no new vertical channel development. These NLDN events may reflect currents flowing through pre-existing channels that were formed earlier in the flash. Additionally, we found that flashes with longer horizontal extent have a higher chance of being reported by the NLDN. In this report, we will summarize our findings to date, and discuss our continued work in this area to explore the relationship between other features of IC flashes observed at VHF and NLDN IC pulse detection. Candidate features include the maximum height, spatial distribution, flash duration, and the maximum vertical velocity of the initial upward leaders.