Infrared and Visible-Range Optical Observations of Lightning at LOG (Lightning Observatory at Gainesville) and Associated Modeling

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Lightning is a transient, high-current electric discharge of typically tens of kiloamperes in air with a flash rate in tens to a hundred per second. Lightning channel is composed of ionized gas or plasma, whose peak temperature is typically 30,000o K, about five times higher than the temperature of the surface of the Sun. Each year, some 25 million cloud-to-ground lightning discharges occur in the United States, and this number is expected to increase by about 50% due to global warming over the 21st century. A lightning strike to an unprotected object or system can be catastrophic. Lightning causes more fatalities than any other thunderstorm-related hazard, such as tornadoes and flooding. Lightning initiates many forest fires, and over 30% of all electric power line failures are lightning related. In the funded research, a new high-speed infrared (IR) framing camera will be employed for the first time at the Lightning Observatory in Gainesville, Florida for lightning observations in conjunction with the existing instrumentations, including the optical systems, electric and magnetic field measuring systems operating in different frequency ranges, and x-ray detector to obtain a view of lightning processes that has never been possible before. The IR camera will allow the imaging of lightning channels inside clouds that generally are not accessible to visible-range cameras. The lightning channel cooling process and the thermal energy input to different parts of the channel will be studied. The optical and corresponding GPS time-stamped electromagnetic field data will be used to develop, for the first time, a non-linear and non-uniform distributed-circuit model, which will allow the investigation of a variety of lightning processes, including the final-jump phase of lightning attachment to ground or grounded object, which has not been documented for natural lightning. This funded research will further advance our understanding of the physics of lightning and its effects with important implications for environmental and climate change research and for mitigation of lightning hazards to people, structures, and systems. An improved knowledge of lightning attachment process is needed for designing adequate protection against lightning and for developing lightning testing standards. This project will involve postdocs and Ph.D. graduate students, as well as international collaborations, including two visiting scholars supported by their home Universities and a Fulbright Scholar. The research findings will be incorporated in the popular University of Florida senior undergraduate/graduate course "Lightning." The PI will continue to engage with high-school science education and public awareness of lightning hazards. Besides the Physical and Dynamical Meteorology area, the results of the project will be useful in other disciplines, including high-energy atmospheric physics, plasma physics, lightning protection and testing, and lightning safety.