Qie Xiushu

Characteristics of a Negative Cloud-to-Ground Lightning Discharge Based on Locations of VHF Radiation Sources

Abstract The lightning very high frequency (VHF) radiation location system based on the short-baseline time-difference of arrival (TDOA) technique provides an effective approach to describe the temporal and spatial development of lightning discharge in two dimensions with high resolution. A negative single-stroke cloud-to-ground (CG) lightning flash was analyzed in detail using the radiation location results and synchronic fast/slow electric field changes. The long-duration preliminary breakdown process appeared to propagate with bi-directional leader channels. The two negative simultaneous discharge channels sloped down with a considerable horizontal component in the lower positive charge region at speeds of about 105 m s-1. The stepped leader was clearly converted from one channel of the preliminary breakdown process and spread downwards with branches. The speeds of the stepped leaders were about 105 m s-1. The K processes after the return stroke could either directly initiate from the start region with negative polarity lightning discharge, or initiate from a new region in the cloud as negative recoil streamers. All K processes propagated along the preceding electrified channel, while not all K processes initiated from the tips of positive breakdowns. The speeds of the K processes were about 106-107 m s-1.

Observation of Lightning Current and Ground Potential Rise in Artificially Trigged Lightning Experiment

Lightning current and ground potential rise (GPR) results of artificially trigged lightning experiment in Binzhou of Shandong Province during the summer of 2006 are described in this paper. The variation of grounding resistance of grounding electrode is analyzed according to the data of experiment. From the waveform of lightning current, it can be found that the process of lightning flash has two return-strokes. The amplitude of the first return-stroke is 41.59 kA with 6.02/20.24 mus waveform, and that of the second return-stroke is 29.59 kA with 4.8/11 mus waveform. The previous study done by other authors on impulse ground resistance is always limited in the laboratory, which can provide the standard impulse current instead of the factual circumstance. Transient grounding resistance (TGR) including two small return-strokes response is obtained. ATP Simulation is used to calculate the impulse grounding resistance which compares to the factual circumstance. There is time difference between peak current and peak voltage, but the simulation can not tell the difference, which means their front time Tf and time to half value Tt are identical. That is because the simulation model did not take the spark discharge and its electrical parameter change into consideration. The results can help study the process of artificially trigged lightning, meanwhile it proposes the necessity to consider grounding electrodes impulse characteristics under lightning current.