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THE ELECTRICAL STRUCTURE OF THUNDERSTORMS 90 8 The Electrical Structure of Thunderstorms Paul R. Krehbiel New Mexico Institute of Mining and Technology Thunderstorms and the lightning that they produce are inherently interesting phenomena that have intrigued scientists and mankind in general for many years. A number of theories have been proposed to explain how thunderstorms become electrified, and many field and laboratory experiments have been conducted to determine the electrical nature of storms and to test the electrification theories. Through this effort we are beginning to understand how electric charge is distributed in storms, but the mechanisms that cause their electrification continue to elude scientists and remain the subject of considerable inquiry and debate. The basic difficulty in determining how thunderclouds become electrified lies in the fact that they are large, complex, and short-lived phenomena that need to be examined both as a whole and in detail to understand how they function. The electrical processes are intimately related to the cloud dynamics or motions and to the microphysics of the cloud, namely, to the populations and interactions of the precipitation, cloud droplets, ice crystals, and other particles that make up the cloud. These important aspects of storms are themselves incompletely known or understood, yet a detailed comprehension of them is necessary to understand the electrification processes. Attempts to simulate possible electrification processes in the laboratory or by theoretical modeling have been helpful in evaluating some theories but have not demonstrated the efficacy of any particular mechanism. This is because thunderstorm conditions are inherently difficult to simulate and are insufficiently understood for us to be confident that we are simulating them properly. At present, further progress in understanding the electrification of thunderstorms, and indeed in understanding their dynamics and precipitation processes as well, requires simultaneous observations of their dynamical, microphysical, and electrical properties. This need has been increasingly recognized in recent years and has given rise to a number of cooperative studies of storms. The cooperative studies employ the latest techniques for internally and remotely probing storms and rely on the combined expertise of university and national laboratory researchers to conduct and analyze the observations. The studies typically use instrumented aircraft and balloons to penetrate the storms, multiple radar systems to measure precipitation strengths and velocities, and ground-based instrument networks for measuring meteorological and electrical quantities. A few research programs have focused on the electrification question, including the ongoing studies at the Langmuir Laboratory for Atmospheric Research in the mountains of central New Mexico and the Thunderstorm Research International Program (TRIP) in Florida and New Mexico. These and other studies have
