利用宽带干涉仪的三维观测数据， 对发生在负地闪继后回击前的不规则脉冲簇事件CPT进行了研究。首先对CPT事件快电场时域波形特征进行了分析， 然后， 研究了CPT事件的辐射源时空发展特征， 并对这些CPT事件、 梯级先导和直窜先导在30~290 MHz频段辐射信号的功率谱密度进行了对比分析。结果表明， 10次CPT事件的快电场脉冲间隔平均值和标准差分别为5.3~9.0 μs和2.7~4.9 μs。CPT事件的击穿过程为负极性击穿， 其发展特征与直窜先导或企图先导没有明显区别。10次CPT辐射源发展速度的统计结果表明， 平均发展速度在3.23×106~1.93×107 m·s-1之间， 平均值为1.02×107 m·s-1， 与企图先导或直窜先导的速度统计结果相当。10次CPT事件在30~290 MHz频段的功率谱密度平均值分别比同次地闪中的梯级先导和直窜先导强1.8~11.6 dB和2.4~12 dB。
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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