The Conductivity And Propagation Property Of Lightning Leader Tip

The propagation properties of lightning leader have an important significance for investigating the physical mechanism of lightning process.The temperature,electrical conductivity and two-dimensional transmission speed(2-D speed)of the lightning leader channel are calculated by using the spectral data and optical pictures from the development process of the eleven cloud-to-ground lightning recorded by high-speed spectrograph in Qinghai.In this paper,the variation characteristics of 2-D speed of seven stepped leaders,two dart stepped leader and six dart leaders are analyzed,and the correlation between their propagation speed and channel conductivity and propagation direction is further studied.It is found that the relative strength of the dart leader spectral line is stronger than that of the stepped leader,and qualitatively inferred that the channel temperature and conductivity of the dart leader is higher than that of the stepped leader.we calculate the channel temperature is around 1.50-1.53×10~4K,the conductivity is 3.83-4.87×10~3S/m,and the 2-D speed is 1.89-6.84×10~5m/s for the three lightning stepped leaders.The temperature,electron densities and electrical conductivity for the stepping part of dart stepped leader are larger than that of the stepped leader,but slightly smaller than that of the dart leader.It can be seen that the temperature of the dart leader is about 7100K higher than that of the stepped leader,and the electron density is on average about 2 orders of magnitude higher than the value of stepped leader.The conductivity of dart leader is on average 0.74×10~4S/m larger than that of the stepped leader,and its corresponding propagation speed is one order of magnitude larger than that of the stepped leader.In addition,at the node or branch point of lightning,the propagation speed decreases obviously,the intensity of ionic lines are abruptly enhanced,the ion line strength of the corresponding spectrum is higher,and the temperature and conductivity of these positions are also higher than other positions of the channel.This is because the local charge accumulation caused by the propagation speed decrease,which makes the electric field and the electron density increase.It is find that the 2-D speed is positively correlated with the conductivity of the leader tip,and the propagation direction of the leader is also an important factor affected its propagation speed,the smaller the angle between direction of the 2-D speed and vertical electric field is,the higher the speed is.These properties are important for explaining the formation and development mechanism of discharge channels.