Field Enhancement by Lightning Strikes to Tall Tower Versus Lightning Strikes to Flat Ground.

When a lightning strikes a high object, the current flows along the object and produces in this way a field component additional to the field radiated from the lightning channel. This additional field component enhances the field compared to lightning to flat ground. In this article, the field enhancement is analyzed for lightning striking the Peissenberg Tower, Germany. The analysis is based on investigations of the far field at distances from 10 to 1000 km. In the computer simulations, the return stroke process is taken into account with the transmission line (TL)-model and the tower is modelled with the computer program CONCEPT II based on the method of moments. In a first step, the pure effect of the tower is analyzed. In this case, the ground is taken into account as perfectly conducting plane. In the next step, the effect of the field propagation is added by introducing an attenuation function based on the solution of Sommerfeld and a far-field approximation of Norton. For fast rising return stroke currents and relatively near distances between 10 and 30 km, the field enhancement may exceed 100%. The field enhancement decreases strongly with decreasing soil conductivity (σ) and increasing distance (s), while the influence of the permittivity (ϵ) is rather small. At a distance of more than 100 km the field enhancement is typically in the range of some tens of percent. This result agrees well with the data of the European lightning location system EUCLID. From EUCLID an average field enhancement of about 20% is reported for lightning striking the Peissenberg Tower. [ABSTRACT FROM AUTHOR]