Characteristic Analysis And Simulation Of Downward Cloud-to-ground Lightning Flashes Around The Canton Tower

Based on optical data of Tall-Object Lightning Observatory in Guangzhou from 2009 to2014,combined with the lightning acoustics and electromagnetic field change waveform data,the distribution characteristics of 119 downward cloud-to-ground lightning flashes in the northwest of Canton Tower within 3 km of 60°sector region were analyzed.Then,based on the two-dimensional random lightning leader model,the protective effects of a single tall building on nearby buildings were simulated and the protective effects of Canton Tower(600m spire building),Canton East Tower(530 m flat roof building),Canton West Tower(440 m flat roof building)and Guangsheng Building(360 m spire building),which were the four tallest buildings in Zhujiang New Town,were compared.Finally,the comprehensive effect of several tall buildings on the distribution of downward flashes was simulated.Results show that:Observation results of distribution of downward flashes in Canton Tower and its vicinity:1)43.7%(52/119)of downward flashes occurred on the four tallest buildings in the area;2)Except 20(16.8%)downward flashes hit Canton Tower,no downward flashes were observed in the area of 0-1 km near Canton Tower.35(29.4%)downward flashes were observed in the area of 1-2 km away from Canton Tower,the buildings lower than 300 m were hit no more than once,the closest stroke point to Canton Tower was about 1.2 km away.64(53.8%)downward flashes were observed in 2-3 km away from Canton Tower.Some buildings with a height below 300 m were hit more than once,up to 5 times;3)Attraction of Canton Tower to downward flashes caused no downward flashes were observed within 1 km of Canton Tower.In the range of 1-3 km of Canton Tower and the downward flash density(except the downward flashes that hit buildings not less than 300 m)gradually increased with the increase of the distance.Results indicated that attraction of high buildings to the downward flashes gradually weakened with the increase of distance.Simulation results of protective effects of a single tall building on nearby buildings: 1)When the downward leader started from the top of the building,probability of lightning hit buildings increased with the increase of height of the building.Lightning strike probability exceed 90% when the height of building reached 200 m,and reached 100% when the height reached 400 m.2)When there was a higher building B near a building A,the protective effectof the building B on the building A increased as the height of the building B increased,the height of the building A or the distance between the two buildings decreased until the building A was completely protected.3)The lightning protection effects of the four tallest buildings in Zhujiang New Town were as follows: Canton Tower was the largest,Canton East Tower was the second,Canton West Tower and Guangsheng Building were the smallest.Influenced by the shape of buildings,the height of Guangsheng Building was lower than that of Canton West Tower,while the protection effects were almost the same.4)There were 8 buildings with a height of not less than 300 m in study area.Except for the four tallest buildings,the lightning strike probability of the other four buildings was only 1%~25% under the influence of higher buildings.In addition,the distance between Canton East Tower and Canton West Tower was about 270 m,and the lightning strike probability of Canton West Tower under the influence of Canton East Tower was 16%.Simulation results of the comprehensive effects of several tall buildings on downward flashes distribution: 1)The simulation results of two groups of buildings(Guangsheng Building,Canton West Tower and Canton Tower;Guangsheng Building,Canton East Tower and Canton Tower)showed that the number of downward flashes hit ground was the least,and the number of downward flashes hit Canton Tower was the highest.Comparing the simulation results of the two groups,it is found that the number of downward flashes hitting Canton East Tower was more than that of Canton West Tower.Comparing the distribution characteristics of downward flashes between the two groups and the attraction ability of isolated buildings to downward flashes,it was found that the attraction ability of Canton West Tower(Canton East Tower)to downward flashes was no less than that of Guangsheng Building,but the number of downward flashes was less than that of Guangsheng Building.2)The range of the starting point of flashes attracted by buildings was defined as the attraction range.The length of attraction range of Canton West Tower and Canton East Tower on the side of Canton Tower was significantly shorter than that on the side of Guangsheng Building.Therefore,the attraction of the Guangzhou Tower to the downward flashes near Canton West Tower(Canton East Tower)led to the number of downward flashes hit Canton West Tower(Canton East Tower)less than that of Guangsheng Building.3)When multiple tall buildings exist simultaneously or in isolation,the length of the upward leader triggered on Canton Tower and Guangsheng Building was longer than that triggered on Canton West Tower and Canton East Tower.