Electromagnetic Environment Associated with Lightning Strikes to Tall Strike Objects

The study of the lightning interaction with tall strike objects has attracted considerable attention of lightning researchers lately. Many lightning measurements including current and associated electromagnetic fields were recently made all over the globe namely in Russia, South Africa, Germany, Brazil, Japan, and Austria. It is a novel area of studies, and the resolution of associated questions will have an impact upon many lightning-related applications such as lightning protection and the determination of lightning parameters from remote field measurements. The main objective of the thesis is to carry out further theoretical investigations and experimental measurements to understand and elucidate recently raised questions on the characteristics of lightning return-strokes to tall structures and their associated electromagnetic radiation. Chapter 2 presents a review on recent progress in the modeling of lightning strikes to tall towers and associated experimental data obtained during the last decade or so. Two types of return stroke models namely the Engineering Models, and the Electromagnetic or Antenna-Theory (AT) models, extended to take into account the presence of a tall strike object are discussed. The Chapter contains also a description of the computational methods for the evaluation of electromagnetic fields generated by a lightning strike to a tall structure, as well as an overview of available data on lightning current and associated electromagnetic fields. The chapter finally highlights some important questions raised by different research groups in the past few years which call for further investigations. These questions are as follows: No systematic theoretical analysis nor experimental data are available for electromagnetic fields in the immediate vicinity of a tall structure struck by lightning. The characterization of nearby electromagnetic fields is particularly important in the analysis of the interaction to nearby electrical and electronics systems. Why do lightning return stroke models not reproduce the far-field zero crossing associated with lightning to tall structures? How should these models be revised to be able to reproduce such an effect? How should the engineering models be revised in order to remove the associated current discontinuity at the return stroke wavefront? It is well-known that the measurements of electromagnetic fields from lightning are affected by the presence of nearby buildings and metallic structures. However, no systematic and quantitative analysis of such an effect is presently available in the literature. The work presented in this thesis addresses all of the above questions. The main original contributions of this thesis, consisting of both theoretical and experimental work, are presented in Chapters 3 through 6. Chapter 3 is devoted to a theoretical description of the signature of electric and magnetic fields at very close distance associated with lightning strikes to a tower. It is shown that