We characterized 205 multiple-termination negative cloud-to-ground (CG) lightning flashes that were imaged by the Fast Antenna Lightning Mapping Array (FALMA) in Japan during the summer of 2017. The parameters we used included termination number, termination distance, fork height, return stroke (RS) number, the interval between the first RS of each termination, the shortest time difference between the strokes at different terminations, and the first RS intensities separated by termination occurrence orders. It was found that the multiple-termination flashes (MTFs) had a termination number ranging from 2 to 5, with the majority (148/205) at 2. The termination distance (with high probability) was between 2 and 4 km, with 10 out of 359 MTF termination distances being longer than 10 km. For most MTFs (146/205), their leader forks for different terminations occurred at a height between 4 and 6 km, indicating that the fork process mainly occurred inside the cloud. The RS number of the MTFs ranged from 2 to 18, with an arithmetic mean (AM) value of 5.8. The interval between the first RS of each termination in the MTFs ranged from 0.5 to 965.3 ms, with an AM value of 225.6 ms, while the shortest time difference between the strokes at different terminations had an AM value of 189.6 ms. The intensity of the first stroke in each termination tended to decrease with increasing termination occurrence orders.
We started a long-term continuous observation of lightning discharges in the Chinese inland plateau region using a fast antenna lightning mapping array (FALMA). During the first year of observation, 2019, we recorded lightning discharges on 25 days in Yinchuan city, the capital of Ningxia. Most of the lightning discharges appeared to occur in the afternoons of individual thunderstorm days in August. We studied the cloud-to-ground (CG) flash percentages, lightning discharge source spatiotemporal distributions, and preliminary breakdown (PB) process characteristics for the two thunderstorm cases that produced the most frequent lightning flashes in 2019 over a wide area. It was found that (1) CG flashes in these two thunderstorms accounted for 28.4% and 32.5% of total lightning flashes, respectively; (2) most lightning discharge sources in these two thunderstorms occurred at temperatures between 5 and −30 °C, with a peak at around −10 °C; and (3) more than 90% of well-mapped PB processes of intracloud (IC) flashes propagated downward. By overlapping the altitudes and the progression directions of the PB processes on the lightning source spatiotemporal distributions, we inferred that the main negative charge of the two storms observed in Ningxia, China, was at a height of around −15 to −25 °C (7 to 9 km) and the main positive charge was at a height of around 5 to 0 °C (2 to 4 km).
We have studied the pulse parameters and peak currents of 17,225 return stroke (RS) events in the cloud-to-ground lightning flashes observed in Chinese inland areas by a multistation mapping system called Ningxia Fast Antenna Lightning Mapping Array. There are a total of 685 positive and 16,540 negative RS events, respectively, producing 8280 and 195,860 pulses at multi stations. It is found that on average, the positive RS pulse appears to have a longer rise time, wider half-peak width, shorter fall time and longer zero-crossing time than the negative RS pulse. The RS peak currents are estimated through time-matching with a modest number of RS from the calibrated lightning location system. The statistical results show that the arithmetic means of positive and negative RS peak currents are 31.5 and 22.8 kA, respectively. Compared to previously reported studies, both the RS pulse parameters and peak currents are significantly different. Particularly, we note that in our dataset, the percentage of positive RSs with peak currents below 10 kA is up to 27%, a significant number which should be taken into account in such types of statistical studies. Additionally, we have further used the data from Gifu, Japan, and Ningxia, China, to verify how distance ranges and observation regions affect the RS characteristics. The results have provided distinct evidence that the distance ranges and observation regions should be at least two of the factors attributing to the statistical disparities among different studies.
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