Thunderstorm Electrification and Lightning Flash Sizes in Meteorological Context (Core Science Lecture)

Lightning gives a thunderstorm its name, and herein the relationship between electrical processes and the rest of a cloud's meteorology are explored. After time, the microscale processes responsible for thunderstorm primary electrification result in net charge regions, which in turn set the stage for cloud and ground discharges of various sizes, energies, and propagation paths. Basic patterns of electrification and lightning are reviewed. They are easily explained by the non inductive, ice-based relative growth rate mechanism of electrification. Studies of storms in all states of mesoscale organization in diverse meteorological environments show variations around these basic patterns, with some storms producing more frequent positive ground strikes and larger fraction of cloud flashes. Microscale details of electrification are known to be sensitive to details of hydrometeor growth rates while the formation of net charge regions depends on how each storm distributes its hydrometeors, including at the scales of turbulent eddies. In these ways, electrical activity is inextricable from the other meteorological aspects of the thunderstorm system. The ability to predict such variability for a population of thunderstorms on a given day is a grand challenge that would provide a stringent test of atmospheric electricity theory and the accuracy of observed or modeled meteorological environments. Illustrations of the variability of flashing behavior in polarity, size, and energy will be drawn from recent field studies, with a view toward the utility of understanding such variability in problem domains from atmospheric chemistry to severe storm nowcasting.