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Simulation of Various Connecting Patterns During the Lightning Connection Process Based on the Stochastic Lightning Leader Model
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摘要: 考虑到下行负极性地闪过程中大多上行正先导发展时不分叉的观测事实，基于已有的闪电先导二维随机模式，改变上行正先导的模拟方案，使其发展时不产生分叉，并对雷击高建筑物过程中下行先导与上行连接先导 (upward connecting leader，UCL) 之间头部-头部连接和头部-侧面连接 (侧击) 的两种形态进行模拟。以高度为440 m的建筑物为例，通过改变下行先导始发点 (高度为1000 m) 与高建筑物的水平距离，模拟高建筑物上雷击过程中先导之间的连接过程，结果表明：当下行先导始发点与高建筑物的水平距离从0增加到700 m时，UCL的长度呈持续增大趋势，UCL受侧击的概率总体上呈先增大后减小的趋势 (在距离为500 m时达到最大值58%)，侧击时UCL连接点以上的部分占整个UCL长度的比例总体呈持续增大趋势 (13%~49%)。Abstract: Considering the observed fact that most upward connecting leaders (UCL) does not branch during downward negative cloud-to-ground (CG) strikes, the simulation scheme of upward positive leaders is modified based on the existing two-dimensional (2D) stochastic lightning model. In addition, two connecting patterns, i.e., the tip-to-tip connecting and the tip-to-lateral connecting (lateral strike) between the downward leader and the UCL are simulated during the process in which lightning strikes tall buildings. Sensitivity experiments are carried out on the connecting process between leaders during the process of lightning striking a tall building by altering the horizontal distance between the initiation point of the downward leader (at a height of 1000 m) and the tall building. Results indicate that when the value of d increases from 0 to 700 m, the probability of a lateral strike for the UCL generally exhibits a trend of first increasing and then decreasing. As the value of d increases, the length of the UCL exhibits an increasing trend, and the ratio of the part of the UCL above the connecting point accounting for the entire length of the UCL upon the lateral strike generally exhibits an increasing trend. The probability of each grounding position is under the influence of the horizontal distance. The UCL initiating from the top of tall structures is longer than that initiating from the ground or the side surface of tall structures. Furthermore, tall structures with different heights are also investigated.
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Key words:
- tall structures;
- connecting point;
- grounding point;
- tip-to-lateral
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图 2 建筑物与下行先导始发点位置的选取
Fig. 2 The building and the selection of initiation positions for the downward leader
图 4 不同位置接地概率随d变化 (a) 与UCL平均长度随d变化 (b)
Fig. 4 Changes of grounding probability at different locations with d(a) and changes of the average length of UCL with d(b)
图 5 d不同UCL受侧击的模拟结果
Fig. 5 Simulation results of the tip-to-lateral connection behavior with different d
图 6 UCL受侧击概率随d的变化 (a) 及R随d的变化 (b)
(R为UCL连接点以上的长度与UCL总长度比值的平均值)
Fig. 6 Changes of probability of tip-to-lateral connection behavior with d(a) and changes of R with d(b)
(R is the average ratio of the length between connection point to the tip of UCL and the whole length of UCL)
表 1 不同位置的接地概率
Table 1 Grounding probability at different locations
d/m 地面/% 高建筑物侧面/% 高建筑物顶面/% 0 0 0 100 100 0 0 100 200 0 1 99 300 0 4 96 400 4 23 74 500 25 34 41 600 54 31 15 700 84 14 2 
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表 2 各位置起始UCL的长度范围
Table 2 The length of UCL initiating from different locations
d/m 地面 建筑物侧面 建筑物顶面 范围/m 平均值/m 范围/m 平均值/m 范围/m 平均值/m 0 44~400 189 100 58~376 187 200 10~24 16 118~428 198 300 24~30 16 134~464 211 400 10~38 18 10~44 18 104~516 245 500 10~58 19 10~64 21 142~569 276 600 10~68 18 10~77 20 157~519 296 700 10~72 18 10~58 16 197~494 317
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表 3 高建筑物顶面起始的UCL长度范围
Table 3 The length of UCL initiating from the top of the tall structure
d/m 头部连接的UCL 受侧击的UCL 范围/m 平均值/m 范围/m 平均值/m 0 44~288 183 74~400 199 100 58~356 179 118~376 198 200 128~428 191 118~390 207 300 134~373 190 134~464 229 400 104~516 239 132~436 251 500 148~508 265 142~569 285 600 157~490 285 187~519 306 700 197~494 307 188~450 320
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表 4 d不同情况下UCL受侧击情况的模拟结果
Table 4 Simulation results of tip-to-lateral connection as the value of d changes
d/m Nt Nl P/% R Lu/m Lc/m 0 400 136 35 0.13 199 27 100 400 165 41 0.17 198 35 200 396 175 44 0.18 207 42 300 384 203 53 0.26 229 66 400 295 149 51 0.26 251 71 500 165 95 58 0.34 285 101 600 59 31 53 0.37 306 110 700 7 2 29 0.49 320 156 注：Nt为接地点在建筑物顶面的次数，Nl为UCL受侧击的次数，P为UCL受侧击的概率, R为UCL连接点以上的长度与UCL总长度比值的平均值，Lu为UCL平均长度，Lc为连接点到UCL头部的长度。
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