地闪近地面形态特征的数值模拟

摘要

As a common phenomenon in nature,lightning can influence living environment and production ex-tremely.With continuous field lightning observation tests and model experiments,the understanding of lightning process is making a great progress,especially for cloud-to-ground (CG)lightning progression process.The spatial propagation of lightning shows characteristics of randomness,which make lightning unpredictable and lightning protection difficult. The influence of different lightning spatial configurations on CG lightning process is studied,including the location of stroke points,the length of upward leader,the tip location of downward leader when up-ward leader trigger,form of lightning attachment process.Based on existing model,a region near to the ground is highlighted and the spatial resolution is improved.A 2-dimension model of CG lightning progress process is developed to simulate different lightning spatial configurations by changing random parameters via using the finite difference method.It shows that the difference of lightning spatial configurations will make the location of stroke points different,and random lightning spatial configurations make the length of upward leader random.The range of length of upward leader is 77 m to 609 m,and it concentrates on 100 m to 200 m.Besides,statistical results show that the length of upward leader triggered from building is longer than that triggered from the ground.It also makes the tip location of downward leader when up-ward leader trigger distribution regularly.The tip location presents ellipsoidal distribution over the build-ing.Also,different lightning spatial configurations will affect the form of CG lightning attachment process.Simulation results emerge three lightning attachment process forms and all can be verified by field lightning observations.All these outcomes show that lightning spatial configuration plays an important role in affecting CG lightning process. In addition,according to a series of statistical analysis,it shows that the length of downward leader and the length of upward leader near the ground have certain linear correlation.The other factors of light-ning have little correlations,such as the length of downward leader near the ground and striking distance, the length of upward leader and lightning horizontal extent.%该文在已有闪电随机放电参数化方案的基础上，截取近地面区域，保持闪电其他基本参数不变，通过改变闪电的空间形态，对同一背景下的闪电进行多次模拟，研究闪电近地面空间形态的差异对闪电击地点位置、上行先导长度、上行先导触发时下行先导的尖端位置及连接过程形态等参数的影响，并探索闪电参数之间的相关性。结果显示：闪电近地面空间形态会使上行先导长度在77～609 m 区间内变化，大部分集中在100～200 m，也会使上行先导触发时下行先导的尖端位置分布在建筑物上空的一个椭球形空间内。同时，闪电近地面空间形态的差异也会使地闪连接形态呈多样性。另外，近地面闪电下行先导长度与上行先导长度有一定的线性相关性，而其他闪电参数相互之间的相关性较弱。这不仅可以加深对闪电空间形态不确定性的理解，同时也对以后的模式建立有一定借鉴意义。