Characteristics of Cloud-to-Ground Lightning Return Strokes in Beijing Based on High Temporal Resolution Data of Fast Electric Field Change

Return stroke waveform characteristics of 304 positive cloud-to-ground (CG) flashes and 1467 negative CG flashes observed during five storms in Beijing region were analyzed based on high temporal resolution data of fast electric field change collected by Beijing Lightning Network (BLNET). Characteristic parameters presented in this work are:The number of strokes per flash, 10%-90% risetime, falling time, full width at half maxmum (FWHM), interstroke interval, peak electric field and the relationship between the interstroke interval and stroke order, etc. The results indicate that the percentages of single stroke in positive and negative CG flashes were 91.1% and 24.2%, respectively. The average number of stroke per flash for negative CG flashes was 3.8 and the max stroke number was 20. The arithmetic means of 10%-90% risetime, falling time, and half-peak width for the 304 first strokes of positive CG flashes were 4.2 μs, 14.5 μs, and 6.2 μs; the corresponding values for the 29 subsequent strokes of positive CG were 3.6 μs, 12.6 μs, and 5.7 μs; the corresponding values for the 1467 negative first strokes were 2.4 μs, 23.9 μs, and 5.3 μs, and the corresponding values for the 4109 negative subsequent strokes were 1.7 μs, 19.5 μs, and 3.4 μs, respectively. In addition, interstroke intervals of positive and negative CG flashes showed a more or less log-normal distribution and yielded the geometric mean values of 106 ms and 59 ms. Moreover, the geometric mean interstroke interval for negative CG flashes of particular multiplicity tended to decrease with the stroke order. Finally, peak electric fields of the 70 positive, 421 negative first, and 789 negative subsequent strokes, when normalized to 100 km, were 11.2 V/m, 7.2 V/m, and 5.0 V/m, respectively. On average, peak electric field for the first stroke was 1.4 times larger than its subsequent counter part for negative CG flashes. However, about 23.5% of subsequent return strokes were stronger than the corresponding first stroke.