Simulation Of Lightning Electromagnetic Fields On The Finite Conductivity Ground

The lightning huge current and quickly electromagnetic field changes would lead great damage in our society, like electric power system, transportation, telecommunications, forestry and other industries. However, the electromagnetic fields changes would be changed depending on the finitely conducing ground,which enables making a greater uncertanties to the the detection of ground lightning, inversion of lightning discharge, LEMP protection works and so on. In this paper,the impact that the finitely conducing ground of propagation paths have on the lightning-generated electromagnetic fields and the lightning dection is studied. The main achievements are as follows:(1) the lightning leader-return stroke model in the case of ideal ground conductivity is analyzed firstly in this paper. by using the Heidler function, Heidler and double exponential function,the four return strokes wave of the triggered lightning experiment were fitted,based on the lightning current fitted parameter,the temporal and spatial distribution characteristics of the Channel charge density and the return stroke electromagnetic fields on ideal ground conductivity were simulated by using MTLL return stroke model.(2) In order to reproduce the V-shape structure characteristics of the close dart leader/return stroke field change, we employ two existing models, one for the'source charge'leader model and the other for MTLL return stroke model, both based on the assumption of uniform leader charge distribution along the channel and the charges deposited by the dart leader are completely neutralized by the following return stroke process. The simulated results show that the return stroke electric field is inversely related with the return stroke speed at early times (within few tens of microseconds of the beginning of the return stroke), the close electric field is independent of speed and the ratio of the leader field to the corresponding return stroke field tends to be equal to-1. Therefore, at early times (within few tens of microseconds) there is often some uncertainty regarding whether the charges deposited by the dart leader are completely neutralized by the following return stroke process based on the difference between the return stroke and the leader field on the ground.(3) the transmission characteristics of lightning electromagnetic fields in lossy ground surface is further studied. the lightning leader model for the case of lossy ground is presented firstly, and the relationship between the ground permittivity and the leader electric fields is analyzed.then the characteristics of the lightning return stroke electromagnetic fields under the case of conductivity of single-layer uniform, horizontal stratified and vertical stratified conductivity of soil is analyzed by using the wave tilt, surface impedance method and Cooray-Rubinstein (CR) and other return stroke electromagnetic propagation algorithm. (4) the site errors is the main factors that affect the Magnetic Direction Finding (MDF) technique.Based on the site error model for optimizing the lightning location data, about thelightning flash samples in Pingliang,Gansu Province and the central area of Inner Mongolia have been corrected and compared with the radar echo larger than 35dBZ.The results show that the uncorrected CG (Cloud-to-Ground lightning flashes) locations are many kilometers apart from the radar echo areas, and the corrected CG lightning locations are very close to strong radar echo area. The site errors of lightning location system can be minimized by this optimizing model.(5) the effects of propagation over finitely conducting ground on the features of radiation component of the electric field time derivatives are investigated. The results show that the peak and the risetime of the electric field time derivative changes significantly in propagating over finitely conducting ground. Furthermore, any correlation that may exists between various parameters could also change significantly due to propagation effects.Consequently, the errors in the calculated position of lightning could be reduced if we can reduce the propagation time delay.The relationship of the risetime and observed distances can be used to estimate the distance of lightning or the propagation path of electrical conductivity. Finally, the modified method is presented for the inversion of lightning current from lightning magnetic field.