Distortion of Electric and Magnetic Fields from Lightning Due to Close-By Metallic Structures

We present experimental waveforms radiated from distant natural lightning recorded during Summer 2006. Electric and magnetic field waveforms have been measured simultaneously on the roof of a building (the Power Systems Laboratory of the Swiss Federal Institute of Technology, Lausanne, Switzerland) and on the ground 2 metres away from it. The fields have been recorded using flat plate antennas (for the E-field) and magnetic loops (for the H-field). The results suggest that the measured electric field on the roof of the building could be enhanced by a factor of 1.7 to 1.9, whereas the electric fields on the ground experience a significant reduction by a factor ranging from 5 to 20. Also, it is shown that for a sensor located on the ground close to a building, the magnetic field component perpendicular to the building can also experience a significant attenuation, presumably due to the effect of the induced currents in the building.