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Three-Dimensional Observation of Chaotic Pulse Train Event in Negative Cloud-to-Ground Lightning Using VHF Broadband Digital Interferometer

LIU Heng-yi1,DONG Wan-sheng1,ZHANG Yi-jun1,ZHENG Dong1, YAN Bi-wu2,SHI Yu-heng3,WU Ting1(1.State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences,Beijing 100081,China; 2.State Grid Electric Power Research Institute,Wuhan,430074,China;3.Beijing Meteorological Bureau,Beijing 100089,China)  
The chaotic pulse train(CPT) events occurred in negative cloud-to-ground flashes were imaged by three dimensions VHF broadband digital interferometers.10 negative cloud-to-ground flash records were analyzed.The characteristics of the fast electric field change waveform of CPT were analyzed.The results show that the mean value and standard deviation of the pulse separations in these chaotic pulse trains are 5.3~9.0 μs and 2.7~4.9 μs,that is consistent with previous result.Then,the spatial and temporal characteristics,power spectral density from 30 MHz to 290 MHz band and pulse train structure of 10 CPT records are analyzed and the results are compared with those of step leader and subsequent leader.It is found that the breakdown process associated with CPT is negative and similar with attempt leader or dart leader.The statistical result shows the average progression speeds of 10 CPT events are about 3.23×106~1.93×107 m·s-1 with the mean value of 1.02×107 m·s-1,that is also similar with that of attempt leader and dart leader.In the 10 records,the average power spectral density of the CPT in the 30~290 MHz band is 1.8~11.6 dB and 2.4~12 dB larger than that of the step leader and dart leader in the same negative cloud-to-ground lightning.
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