Return Strokes with Abnormal Electric Field Change Waveforms

We have studied 189 return strokes which exhibited abnormal waveforms. We classified these return strokes into 4 types according to their waveforms. Compared to ordinary return strokes, the first type of abnormal return strokes have similar rise time, but much shorter fall time, so RS pulse waveforms appear much narrower. It appears that this type of return strokes are associated with power transmission towers. The second type have a much longer rise time but shorter fall time. The third type have a symmetrical waveform. Both the second and the third types of return strokes are much weaker than ordinary return strokes. The fourth type have two RS waveforms within a time of less than 2 ms. This type of return strokes have two ground terminations with a distance mostly less than 2 km. The return stroke at the first termination is usually stronger than that at the second termination.