Evaluation of the cooray-rubinstein formula for distances farther than a few kilometers using the parallel FDTD method

In this paper, a parallel finite difference time domain (FDTD) code is developed for the calculation of the horizontal electric field above ground for three distances of 2 Km, 5 Km and 10 Km from the return stroke channel. An electromagnetic model of lightning is adopted for the purpose of simulation. The obtained results are compared with those simulated by Cooray-Rubinstein formula (CR). The effect of ground's conductivity on the electric field value is also investigated. The results show that the accuracy of CR formula decreases as the ground's conductivity decreases or distance of observation point from the lightning channel becomes larger.