Observation And Occurrence Regularity Of Chaotic Pulse Trains In Lightning

Chaotic pulse trains (referred to as CPT) discharge event is an important research object in physic field of lightning, and its strong HF radiation and electromagnetic protection of lightning are closely related. Use data of fast and slow electric field and cloud-to-ground (CG) lightning location, this study analyzes distribution characteristic, occurrence regularity and relationship with the lightning discharge of CPT events in lightning discharge process. This study is a part of "Broadband Comprehensive Observations and Physical Processes Research of CPT Events in Lightning" of the National Natural Science Foundation of China (Grant No.41205002). The main conclusions are as follows:1. Universality of CPT eventsResearch shows that CPT events can occur in negative CG lightning, cloud lightning and positive CG lightning.75.2% of negative CG lightnings are accompanied by CPT discharge events, and CPTs can occur before the first return stroke, between strokes and after the last return stroke. CPT discharge events are also occur in cloud lightning(12.1%), and CPTs mainly occur in the final and active stages, especially occur in the final stages of cloud lightning, a proportion reaching 86%. In addition, characteristics of CPT events in the positive CG lightning are similar to which in negative CG and IC lightning.2. Characteristic of CPT events in discharge waveformAccording to the relative position of CPT events and return strokes, CPTs could be divided into two categories. The first is CPT-c which occurs prior to subsequent stroke immediately, and the second is the CPT which occurs a few milliseconds to several tens of milliseconds prior to return strokes, and the second includes for CPT-b before the first return stroke, CPT-i prior to subsequent strokes and CPT-a after the last return stroke. CPT events have four distributions prior to subsequent strokes:single CPT-c, single CPT-i, CPT-c and CPT-i occur concurrently, and several CPT-is occur concurrently. Single CPT-c is the most common,39.4% of subsequent strokes are preceded by Single CPT-c. In addition, a certain percentage of several CPT-as occur concurrently after the last return stroke. The vast majority of CPTs are CPT-cs and CPT-is in negative CG lightning, CPT-c has higher probability of occurrence, and duration time of CPT-c is longer than CPT-i.3. Relationship between CPT events and number of strokes, order of strokes, current intensity of lightning(1) Number of strokes is mainly in 3 times and concentrates in the 2 to 6 times in negative CG lightning with CPT events, and other without CPT is mainly in a single and under 4 times. However, the number of strokes concentrates in the 1 to 3 times in negative CG lightning with CPT-a after the last stroke, and is also mainly in a single.(2) With the increase the order of subsequent strokes, there is a decreasing trend for the occurrence of CPT.(3) CPT events are more likely to occur in negative CG lightning with the stronger current intensity. Average current intensity of negative CG lightning with CPT is 52.28kA, and other without CPT is 36.53kA.4. Correlation between CPT events and physical processes of lightning69.3% of CPT-is prior to subsequent strokes and CPT-as after the last return stroke and most of CPTs accompanied by the final stage in cloud lightning superimpose on the rising or falling stage of negative or positive polarity pulses on K change, and the pulses width is about a few milliseconds. Moreover, very flew of CPT-as and CPTs accompanied by the final stage in cloud lightning both superimpose on the dipolar pulses, and the pulses width is also about a few milliseconds. These CPT events may occur on the same type of discharge events in cloud.5. Similarities and differences of CPT events in different regionsThe vast majority of the characteristics and occurrence regularity of CPT events in negative CG lightning have good consistency both in Beijing and Guangzhou. However, due to differences of the charge structure of thunderstorm in the two regions, the occurrence of CPT events has certain differences. Whether average duration time of CPT-cs, CPT-is and CPT-as in negative CG lightning in Beijing are longer than in Guangzhou. In addition, proportion of CPT-c in negative CG lightning in Beijing is higher than in Guangzhou.