9726100 Rakov While the phenomenon of lightning has been observed for some time, many aspects are unknown. The overall objective of this research is further improvement in the existing knowledge of the physical processes comprising the lightning discharge. Both experimental and theoretical studies are planed. The experimental studies will be conducted at the International Center for Lightning Research and Testing at Camp Blanding, Florida, and at the Lightning Observatory on the University of Florida campus in Gainesville. Camp Blanding contains unique facilities for artificial lightning initiation (triggering) from overhead thunderclouds. For both triggered and natural lightning discharges, electric and magnetic fields will be measured. Channel-base currents will be additionally measured for triggered lightning. Optical images of lightning channels will be obtained with a variety of video, still, and streak cameras, and with a digital optical system. GPS timing will allow the correlation of these measurements with the National Lightning Detection Network reports and to the occurrence of Schumann resonance transients. Attempts to initiate and characterize more energetic and potentially sprite-producing positive lightning will be made. Detailed mechanisms of lightning initiation from an ungrounded object and of lightning attachment to ground will be studied. Measurements of electric and magnetic fields at eight stations, seven of them between 5 and 500 meters of the triggered-lightning channel, will be used to infer the distribution of charge density and current on the lightning channel and to validate or refute existing lightning models. The first attempt to study experimentally the lightning energy in order to resolve the long-standing controversy on its magnitude will be made. Overall, the results of the proposed research will provide new insights into the physics of various lighting processes with implications for other areas of Atmosp heric Sciences, including atmospheric chemistry (energy available for trace gas production by lightning) and the interaction of lightning with the upper atmosphere (in particular, the production of sprites by positive lightning). ***
