空间电荷分布特征对云闪传播行为的影响

Effect of Distribution Characteristic of Space Charge on Propagation Behavior of Intra-Cloud Lightning Discharge

在已有的随机放电参数化方案的基础上,建立了雷暴云电荷分布,并进行二维高分辨率闪电放电的模拟试验,定量探讨了雷暴云的空间电荷分布特征对云闪传播行为的影响,结果表明:(1)雷暴云顶部的屏蔽层电荷以及底部正电荷区会限制触发于雷暴云主正、负电荷区的云闪正、负先导的垂直传播范围,使云闪通道在一定垂直范围内传播,并最终趋向于沿水平方向传播;(2)电荷区的电荷密度或分布范围的增大都会导致云闪通道长度增大,但增大方式不同,电荷密度主要是通过增加高密度中心附近的通道分枝数,并且通道长度随电荷密度的增加呈非线性增大,分布范围则是通过扩展通道的水平传播范围,并且通道长度随分布范围的扩大呈线性增大;(3)电荷区电荷密度的增大会增加云闪通道的分枝数,尤其在高密度中心附近,最终使云闪通道的分形维数呈增大趋势,但基本上不会改变云闪通道的双层分枝结构,电荷区分布范围的扩大则不影响云闪通道的分形维数。

Based on the existing stochastic lightning parameterization scheme,a thundercloud charge structure was set up in the paper and two- dimensional fine-resolution lighting discharge simulations were performed to quantitatively investigate the effect of distribution characteristic of space charge in thunderstorms on propagation behavior of intra-cloud lightning discharge.The results show:(1) The screening charge layer at top of thunderstorm and the lower positive charge region will constrain the vertical propagation range of positive and negative leaders of intra-cloud lightning that are triggered between the main positive and negative charge regions.Thereby,the channels of intra-cloud lightning can only propagate in a certain vertical range and tend to propagate horizontally in the end.(2) The increase of charge density or distribution range of charge region both will increase the channel length of intra-cloud lightning,but in different way.The charge density increases the channel length mainly by increasing the channel branches near high charge density center,and they have a nonlinear relationship,while the distribution range increases it by extending the horizontal propagation range of channels,and they have a linear relationship.(3) The increase of charge density of charge region will increase the number of branches of intra-cloud lightning channel,especially near the high density center,which makes the fractal dimension of intra-cloud lightning channel show a trend of increase,while the bi-level branched channel of intra-cloud lightning will never be changed.The increase of distribution range of charge region will do not affect the fractal dimension of intra-cloud lightning channel.