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APPLICATION OF ADVANCES IN LIGHTNING RESEARCH TO LIGHTNING PROTECTION 61 5 Application of Advances in Lightning Research to Lightning Protection Martin A. Uman University of Florida INTRODUCTION Significant advances in lightning protection have been made during the last decade. These advances have been a result of progress in two general areas of lightning research: (1) lightning phenomenology, including the technology for determining real-time strike locations, and (2) lightning physics, particularly the characteristics of return stroke currents and electromagnetic fields (see Krider, Chapter 2, this volume, for a description of the return-stroke phase of a lightning flash, as well as of the other salient events that make up the flash). (1) By phenomenology, we mean those characteristics of thunderstorms that are associated with numbers of lightning events, as opposed to the physical properties of the individual events. A phenomenological parameter of particular interest is the average lightning flash density, that is, the number of lightnings per square kilometer per year (other units are possible) as a function of location. This parameter represents the starting point for almost all lightning protection designs (for example, the lightning overvoltage protection of utility power lines) because the number of lightning failures per year for which a system is designed is directly proportional to the number of ground flashes per unit area per year. Real-time identification of phenomenological parameters such as the total number of lightning events per storm and the lightning flashing rate is now possible with newly developed detection equipment. This equipment also makes possible real-time decisions on utility system repair and repair preparation, early warning and detection of lightning-caused forest fires, and a variety of other warning functions in situations that allow protective action to be taken, such as launches at the NASA Kennedy Space Center. (2) When an object (e.g., aircraft, building, powerline, or person) is struck directly by lightning, or is exposed to the intense electromagnetic fields of a nearby flash, the potentially deleterious currents and voltages that appear in the object are determined by the physical characteristics of the lightning currents and fields and by the electric characteristics of the object that is struck. For example, it is thought that, to a first approximation, the voltages that are induced in electronics within an airborne metal aircraft that is struck by lightning are indirectly initiated by the fastest part of the current rate of rise. This fast change in current induces resonant oscillations on the metallic exterior of the aircraft (like a pestle striking a bell) that are then coupled inside the aircraft via holes or apertures, such as windows, in the conducting metal skin. Lightning protection is currently of considerable concern for the latest generation of military and commercial aircraft that operate with low-voltage computer circuits and have lightweight ep