An Extension of Cooray-Rubinstein Formula on the Calculation of Horizontal Electric Field from Inclined Lightning Channel

An approximate method to calculate the horizontal electric field from inclined lightning channel in frequency-domain was proposed based on the extension of Cooray formula and Cooray-Rubinstein formula. Validations of these two extended formulas were both performed by comparing their calculation results with those obtained by the numerical solution of Sommerfeld's integrals using Bannister approximations. The results have shown that both the accuracy of these two extended formulas are mainly related to the observation distance and the ground conductivity, and will increase with the increasing ground conductivity and observation distance. The extended Cooray formula could predict the horizontal electric field at ground level accurately at the distance beyond 100m. And the extended Cooray-Rubinstein formula could yield an acceptable approximation on the above-ground horizontal electric field with the exception of the observation point at close range under poor ground conductivity less than 0.0001S/m.