Occurrence regularity of CPT discharge event in negative cloud-to-ground lightning

Occurrence regularity of chaotic pulse trains (CPT) discharge event in negative cloud-to-ground (CG) lightning during six thunderstorms are analyzed in this paper. Results show that CPT is a common phenomenon throughout the negative CG lightning discharge process, 243 times of CPT discharge events occurs during 323 negative CG lightning, a proportion reaching 75.2%. CPT in negative CG can occur before the first return stroke, between the strokes, and after the last stroke. The proportion of 66.7% of the total subsequent strokes is preceded by CPT, and CPT occurs after 11.5% of the total last strokes. It is also found that there are four distributions prior to subsequent strokes: single CPT-c (CPT connecting with subsequent strokes), single CPT-i (CPT occurring in an interval between CPT and return strokes), CPT-c and CPT-i occur concurrently, and several CPT-is appear concurrently. Single CPT-c is the most common, 39.4% of subsequent strokes are preceded by single CPT-c, and several CPTs are easier to occur before the first and second subsequent strokes, which are respectively the corresponding strokes 9.4% and 7.7% of the total number. With the increase of the order of subsequent stroke, there is a decreasing trend for the occurrence of CPT, and in addition to the previous two subsequent strokes, the number of CPT-c is obviously greater than CPT-i before the others. In addition, CPT-i and CPT-a both occur to add on the negative CG K-change, and some also correspond to the process of J-change in the slow electric field wave.