Effect Of The Tall Buildings On The Lightning Electromagnetic Environment

In this paper, we analyze the effect of the tall buildings on the lightning electromagnetic environment by using finite difference method and finite-difference time-domain (FDTD) approach, and establish both three-dimensional thunderstorm atmospheric electric field calculation model and return stroke electromagnetic field calculation model. The thunderstorms electric field and the cloud-to-ground lightning return stroke electromagnetic field around buildings are calculated respectively by this two models. The results of study mainly in the following two aspects:First, we analyze the effect of the tall buildings on the thunderstorms electric field by using finite difference method, and find that when the main charge region of thunderstorm is high, the atmospheric electric field on the ground surface in tens of meters scale can be approximated as a uniform field. The atmospheric electric fields are greatly affected by surrounding buildings and less affected by thunderstorm cloud charge structure. The electric field at the corner of the building is larger than that at the flat roof area and the ground surface. The vertical electric field at the top of the building increases linearly with the building’s height. For example, the field magnitude at the top of the building (at the center point of its flat roof) with plan area S=40×40m2and height h=10,20,50or100m is about1.4,1.7,2.8or4.5times greater than those on the ground surface in the absence of the building, respectively. The field magnitude at the ground level in the immediate vicinity of the building is reduced relative to the case of no building, with this shielding effect becoming negligible at horizontal distances from the building exceeding about3.5times of the height of the building. Due to the mutual shielding effect of buildings, the electric field in the middle area of the buildings is smaller. There also exists the electric field shielding effect at the top of the building with the higher building nearby, and when the greater height difference, the closer distance, the impact is greater.Second, we analyze the effect of the tall buildings on the cloud-to-ground lightning return stroke electromagnetic fields by using finite-difference time-domain (FDTD) approach, and find that the impact of buildings on the return stroke electric field is obvious, and magnitudes of magnetic field are not much influenced by the presence of the building of height hb≤100m (difference is less than10%). The vertical field magnitude at the top of the building (at the center point of its flat roof), which is50m wide and h=20,50or100m height, is about1.3,1.7or2 times greater, and the horizontal electric field is about0.9,0.8or0.7times smaller than those on the ground surface with no buildings, respectively. Considering different ground conductivities (0.1and0.001S/m), we find that the horizontal electric field at ground level is obviously affected by the ground finite conductivity, manifested in the amplitude and polarity, but not significantly dependent on the building distribution. For an above-ground observation point at the considered distance, the horizontal electric field is significantly dependent on the location of observation points and building.