Numerical Simulation Of Lightning Initiation And Discharge Characteristics Under Pocket Charge Distributio

A large number of studies based on observations have proposed that the extension scale of lightning channels is closely related to the charge distribution pattern,and this small and frequent lightning in the strong convection area is likely to be formed in the pattern of charge pockets.In order to verify that such cloud flashes can be formed under the background of pocket charge,and give the general law of lightning initiation and discharge under this charge distribution pattern,in this study,the lightning discharge parameterization scheme was coupled into the double-layer uniform pocket charge model and the non-uniform pocket charge model respectively,and a large number of random simulation tests were carried out,focusing on discussing the similarities and differences of lightning initiation characteristics and discharge behavior under different charge backgrounds.The simulation results largely support the conclusions given by observations,which strengthens the understanding of the existing research results in relevant fields.Simulation results indicate that:1.Under the double-layer uniform pocket charge model,different charge backgrounds are obtained by changing the pairs of charge regions while fixing the total scale of the charge region.The simulation results show that with the increase of charge pairs,the charge concentration and total charge quantity required for lightning start-up increase.The axial ratio of each small charge region is the key factor affecting the lightning initiation behavior.When the vertical and horizontal radii of the small charge region are close,the lightning can develop horizontally.In addition,the spatial configuration relationship of multiple pairs of charges and the runaway breakdown threshold,these two key factors also make the lightning starting position and probability different in the horizontal and vertical directions in each case.The characteristics of lightning discharge are also closely related to the characteristics of the charge region.The development range of the leader is limited by the horizontal and vertical range of the charge region,and the size of the discharge region decreases significantly with the decrease of the charge region area.The spatial characteristics of lightning are limited by the geometric characteristics of small charge region.Besides,the distribution of charge regions significantly affects the development shape of lightning.Compared with the previous charge structure(flat ellipse),when the vertical and horizontal radii of the small charge region are equal,the variation range of initial leader angle is significantly increased,and the number of horizontal development cases is significantly increased.2.Under the non-uniform pocket charge model,different charge backgrounds are obtained by using different charge concentration distribution forms.The simulation results show that the amount of charge contained in the charge region is an important parameter for lightning initiation.Once the charge concentration decays too fast with distance,the area of high charge density is limited to a very small range,and the amount of charge contained in the charge region is too small,which will limit the start-up of lightning.It also shows that there is a certain limit to the degree of chaos in the charge area.In addition,the spatial configuration relationship of multiple pairs of charges,the size of small charge region and other factors also make the lightning starting position and probability different.Under this charge distribution,it is also evident that the horizontal and vertical range and size of lightning are closely related to the scale of charge region,and the closer charge center further limits the development range of the leader.The distribution patterns of initial leader angle and total length of leader channel are closer to the observed results.In addition,there is a significant positive correlation between the total step length of positive or negative leader and the distance from the initiation point to the negative or positive charge center,but the correlation between the total step length and the amount of negative or positive charge is weak.Besides,there is a weak negative correlation between the average step length of the negative leader and the initial altitude.